Visual Basic 1

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2 Visual Basic 2 Introduction To Visual Basic Microsoft Visual Basic is the fastest and easiest way to create applications for Microsoft Windows. Visual Basic provides us a complete set of tools to simplify rapid application development. The name Visual Basic has two parts the Visual part refers to the method used to create the graphical user interface (GUI). Rather than writing numerous lines of code to describe the appearance and location of interface elements, you simply drag and drop Rebuilt objects into place on screen. If you ve ever used a drawing program such as Paint, you already have most of the skills necessary to create an effective user interface. The Basic part refers to the BASIC (Beginners All-purpose Symbolic Instruction Code) language. Visual Basic has evolved from the original BASIC language and now contains several hundred statements, functions, and keywords, many of which relate directly to the Windows GUI. Features Of Visual Basic Visual basic is a tool that allow us to develop window application. It is also called window based programming language. Ready to use component: The main advantage of VB is ready to use component. This environment displays a list of available component. Robust and Powerful: VB make use of GUI for creating robust and powerful application. Hiding the complexity: VB is a better programming language because it hide the complexity from the user and provide an abstract view to the programmer or user. Common programming platform : VB provides a common platform which can access all MS office applications. Wizards: VB also provides wizards that can automate task or even coding. Reusability of code : it is a greatest feature of VB that save time and efforts of programmer and user. Reduce the need of error checking: user can make own life easier and reduce the need of error checking in program by asking the user to select from the list, check an option, use a scrollbar, click on a button. Attractive environment: VB provide us menus, icons, button, scrollbar, and other tool and we make full use of them in our programming. Quick Development: VB offers many tools that provide us quick and easy way to develop application.

3 Visual Basic 3 Easy and convenient procedure: VB s easy and convenient procedure makes VB an interesting and popular language. Visual Basic Integrated Development Environment Here IDE refers to integrated development environment. VB is not just a programming language. It is an IDE in which we can run, design and test and debug our application. IDE is a term that is used in the programming world to describe the interface and environment that we use to create our application. It is called integrated because we can access all the development tools that we need from one screen called an interface. The Visual Basic integrated development environment (IDE) consists of the following elements. Menu Bar: Displays the commands or options we use to work with Visual Basic. VB IDE consists various menus such as File, View, Edit, Project, Format, or Debug, Window, and Help etc. Context Menus: Contain shortcuts to frequently performed actions. To open a context menu, click the right mouse button on the object you are using. The specific list of shortcuts available from context menus depends on the part of the environment where you click the right mouse button. For example, the context menu displayed when you right click on the Toolbox lets you display the components dialog box hide the Toolbox, dock or undock the Toolbox, or add a custom tab to the Toolbox. Toolbars: Provide quick access to commonly used commands and tools in the programming environment. By default, the standard toolbar is displayed when we start Visual Basic. You click a button on the toolbar once to carry out the

4 Visual Basic 4 action represented by that button. Additional toolbar for editing, from design, and debugging can be toggled on or off from the Toolbars command on the view menu. Toolbox: Provides a set of tools or controls that we use at design time. We may place or draw controls on a form. In addition to the default toolbox layout, we may add or remove some other tools by right clicking on toolbox bar. Project Explorer Window: A project is the collection of files we use to build an application. Project explorer window provides a quick reference to various element of project such as form, classes, and module. The project components are organized in the folder. Property Window: A property is a characteristic of an object such as size, caption, position or color. Property window lists the property settings for the selected form or control. We may change these property values as per our application requirement. There are two kind of properties in property window called as runtime property and design time property. Form Layout Window: It is used to determine the initial position of the form in our application at run time. The Form Layout window allows us to position the forms in our application using a small graphical representation of the screen. Form Designer: Serves as a platform or window or dialog box that we customize to design the interface of our application. We can add controls, graphics and pictures to a form to create the look you want. Each form in your application has its own form designer window. Code Editor Window: Serves as an editor for entering application code. A separate code editor window is created for each form or code module in your application. VB provides a smart editor which has the feature of auto complete and auto correct. Immediate, Locals and Watch Windows: These additional windows are provided for use in debugging our application. They are only available when we are running our application within the IDE.

5 Visual Basic 5 Visual Basic Tool Box: The toolbox contains a set of controls that are used to place on a form at design time to create the user interface area. Additional control cab be included in the toolbox by using the components menu item on the project menu. The tools are described below. Tools in the Visual Basic Toolbox Icon Tool Name What This Tool Does Pointer Selects objects Picture box Label Text box Frame Command button Check box Option (or radio) button Combo box List box Horizontal scroll bar Vertical scroll bar Timer Drive list box Directory list box File list box Shape Line Image box Data control OLE Draws a box to display graphics Draws a box to display text Draws a box that can display text and let the user type in text Groups two or more objects together Draws a command button Draws a check box Draws a radio button Draws a combo box Draws a list box Draws a horizontal scroll bar Draws a vertical scroll bar Places a timer on a form Draws a drive list box that displays all the disk drives available Draws a directory list box that displays a directory on a particular disk drive Draws a file list box that displays files in a specific directory Draws a geometric shape such as a circle or a square Draws a line Draws a box to display graphics Draws a control to link a program to a database file Draws a box to insert an OLE object Event Driven Programming: MS Windows uses a GUI as VB programming. In VB we use form window and tool box to design GUI. VB programs are built around events. Events are various things that can happen in a program. In other words an event is a user or system generated activity for example mouse click, or change event. A program which responds

6 Visual Basic 6 according to occurrence of event is known as event driven program. The process, technique and code used to generate event driven program is called event driven programming. In VB almost every control has its own events and event methods. We may use these methods to execute our application. Some most commonly used controls and their events are given below. Mouse Events: The events triggered by mouse actions are the most common events in programming with VB. Most of the elements of the user interface can be manipulated with the mouse. Some popular mouse events are given below. click or double click event: the click event occur when the user click the left mouse button, the double click event takes place when the user double clicks the left button. mouse down and mouse up: the mouse down event take place when the mouse button is pressed and mouse up event takes place as it is released. mouse move: this event takes place as the mouse is moved over a control. Keyboard Event: keyboard events are generated by key strokes and key combinations. Some common keyboard events are given below. Key down or Key up: the key down event is triggered when a key is pressed and the key up event is placed when a key is released. Key press: most programs use the key press event to find out which key was pressed. The key press event is used frequently to write keyboard handler for text boxes. Form Event: We know form is designed as a window or a dialog box so it has several events as given below. Initialize : this event is fixed before the form is loaded or display. Load : The load event performs the action that are required before a form is displayed. It is used to make control on the form. Activate or deactivate: these events are triggered when the user move between two or more forms with in the same application.

7 Visual Basic 7 Types of VB Project: There are different types of project or application that can be created in VB. That are as follows. Standard exe form:- a standard exe project is a typical (mainly used) application. This is the main type of project that we can use create the application. Active X exe or active X DLL (Dynamic linking library):- these type of project are available with the professional addition. Active x components are OLE automation servers and basic code building component that do not have a visible interface and that can add special functionality to our application. Active x control:- the type of project is also a facture of the professional addition, use it to develop our own active x control. Active x control such as text box or command button control is a basic element of user interface. Active x document exe, active x document dll:- active x document are VB application that come run in the environment of a container that supports hyperlink such as internet explorer. VB application wizard, VB wizard manager:- The application wizard fakes( last) is through setting up to seldom of new application means by application wizard we can create same application by using wizard without any different, we can select an applicator that kind of we want to create on then click on next button or wizard and we get our application but creating the application by wizard for modify the seldom more created by the wizard is just as difficult as developing own application from starting. The wizard manager let us our own. A wizard is a sequence of window that collects information from user. After the user fills out all the windows the wizard products to of build on application. Install software or carry out in automated operation for end user. Data-project:- this is a feature of the enterprise addition and it does not correspond to a new project type. Its identical to the standard exe project type but it automatically add the controls that are used in accessing databases to tool box, it also add the data base active x designers to the project explorer window. The active x designers and manipulating data bases and generating reports. DHTML application:- VB 6.0 allows us to build dynamic HTML pages. That can be displayed in the browser window on a client computer. IIs application (internet information server):- VB 6.0 allows us to build application that run on the web server and internet with client over the internet with the IIS.

8 Visual Basic 8 ADD- Ins:- we can create our own add-ins for the VB. Add Ins are special command we can add to visual basic menus. (They usually appear under the add ins menu. VB enterprise addition controls:- its simply create a new standard ex project and loads all the tools of the enterprise addition of VB. Introduction To Visual Basic Variables In mathematics variables are the values which may change time to time. In context of computer variable is a name or place holder of memory where we can store a value temporarily. In VB, we use variables to temporarily store values during the execution of an application. Variables have a name (the word you use to refer to the value the variable contains) and a data type (which determines the kind of data the variable can store). Declaring Variables: To declare a variable is to tell the program about it in advance. We declare a variable in VB with the Dim statement. We supply a name for the variable and data type of variable: Dim variablename [As type] Variables declared with the Dim statement within a procedure exist only as long as the procedure is executing. When the procedure finishes, the value of the variable disappears. In addition, the value of a variable in a procedure is local to that procedure that is, you can t access a variable in one procedure from another procedure. These characteristics allow you to use the same variable names in different procedures without worrying about conflicts or accidental changes. As we name the variable we must take care of following things: Must begin with a letter. Can t contain a period or special type character. Must not exceed 255 characters. Must be unique within the same scope, which is the range from which the variable can be referenced a procedure, a form, and so on. The optional As type clause in the Dim statement allows you to define the data type or object type of the variable you are declaring. There are other ways to declare variables: Declaring a variable in the Declarations section of a form, a standard, or class module, rather than within a procedure, makes the variable available to all the procedures in the module. Declaring a variable using the Public keyword makes it available throughout your application.

9 Visual Basic 9 Declaring a local variable using the Static keyword preserves its value even when a procedure ends. Constants also store values, but as the name implies, those values remain constant throughout the execution of an application. Using constants can make your code more readable by providing meaningful names instead of numbers. There are a number of built-in constants in Visual Basic, but you can also create your own. In VB we can declare constants using const keyword. const constantname [As datatype] = value const salary as integer = Visual Basic Data Types: Data types define the type of information the variable stores. By default, VB uses the Variant data type. Some examples of data types include String, Integer and Currency. Numeric Data Types: Visual Basic supplies several numeric data types Integer, Long(long integer), Single (single-precision floating point), Double (double-precision floating point), and Currency. Using a numeric data type generally uses less storage space than a variant. If we know that a variable will always store whole numbers (without fractional part) we should declare it as an Integer or Long type. If the variable contains a fraction, declare it as a Single (single-precision floating point), Double (double-precision floating point), or Currency variable. The Currency data type supports up to four digits to the right of the decimal point and fifteen digits to the left; it is an accurate fixed-point data type suitable for monetary calculations. Floating-point (Single and Double) numbers have much larger ranges than Currency. The Byte Data Type: If the variable contains binary data, we should declare it as an array of the Byte data type. Using Byte variables to store binary data preserves it during format conversions. The String Data Type: If we have a variable that will always contain a string and never a numeric value, we can declare it to be of type String: Private S As String we can then assign strings to this variable and manipulate it using string functions: S = Database S = Left(S, 4) The Boolean Data Type: If we have a variable that will contain simple true/false, yes/no, or on/off information, we can declare it to be of type Boolean. The default value of Boolean is False.

10 Visual Basic 10 The Date Data Type: Date and time values can be contained both in the specific Date data type and in Variant variables. The same general characteristics apply to dates in both types. Array Array is a set of sequentially arrange similar elements of same name and same data type. Array provide a compact and efficient way for handling blocks of data. Each element of the array has a unique identified number. That is called index number. Index number starts from zero. Array Declaration: Array must be declared with the dim statement followed by the name of the array and maximum size (number of elements) of the array. Dim a(5) As Integer Dim a(1 to 5) As Integer Using the above example a is the name of array that can hold values. A(0) is the first storage place which store first value and a(1) store second value and so on. Types of Array: Fixed size array:- array which always remain same size known as fixed size array there are three way to declare a fix size array depending on the scope we want the array to have. One D array (single dimension array):- by declaring a single dimensional array user have to specify the size of array in the parentheses ( ). These arrays are array that have only one subscription that represent a list values. Dim a(1 to 10) As Integer Dim i% For i=1 to 10 InputBox ( enter number ) Next For i=1 to 10 Print a(i) Next Two D or multidimensional array :- in this type of declaration the user have to specify two argument. First indicates the rows in an array and second argument indicates the number of column means it create a matrix. Dim a (1 to 3 1 to 3) as integer Dim i%, j% For i=1 to 3 For j=1 to 3 A(i,j)= InputBox ( enter number ) Next Next For i= 1 to 3 For j= 1 to 3 Print a(i,j) Next

11 Visual Basic 11 Next Dynamic array: instead of making an array large enough of hold the maximum number of data user can use a dynamic array. Because dynamic array can be recreated during the execution. So dynamic array can be reused dynamically at run time. We can declare dynamic array with public statement or dim statement at the module level or a static or dim statement in procedure. redim dynarray(x=1) The redim statement can used only in procedure. It process the application to carry out an action in run time. Control Array : In Visual Basic, a control array is a group of related controls in a Visual Basic form that share the same event handlers. Control arrays are always single-dimensional arrays, and controls can be added or deleted from control arrays at runtime. One application of control arrays is to hold menu items, as the shared event handler can be used for code common to all of the menu items in the control array. Control arrays are a convenient way to handle groups of controls that perform a similar function. All of the events available to the single control are still available to the array of controls, the only difference being an argument indicating the index of the selected array element is passed to the event. Hence, instead of writing individual procedures for each control (i.e. not using control arrays), you only have to write one procedure for each array. Collection: Arrays are convenient for storing related data but accessing separate elements can be a problem, means a collection object is an ordered set of items that can be referred as a unit. The collection object provide a convenient way to refer related group of items. The collection can be created as follows: Dim city as new collection Once a collection is created member can be added using the add method and can be removed using the remove method. Specific member can be returned from the collection using the item method. Methods of collections: collection object provide three methods and one property. 1. ADD method:- item to the collection. 2. Remove method:- Remove or delete items from the collections by key. 3. Item method:- return to a item by key. Property of collection: 1. Count:- return the number of items in the collection detail of all items. Adding an item to collection: add item method has the following syntax:- Collection Add value key before/after Example: dim temp as new collection temp add 35 Calcutta

12 Visual Basic 12 temp add 40 Mumbai temp add 50 Delhi before Calcutta Adding a new element to a collection assign its value to the value arrangement and its key to the key arrangement. In the above example 35 is the value to be put in the temp collection and the string Calcutta is the new item key. Returning an item: we can return a specific member of collection either by position or by key. Example: Dim temp as new collection Temp add 35 Calcutta Temp add 40 Mumbai Temp add 50 Delhi Calcutta Dim a as integer a=temp.item( calcutta ) a=temp.item(1) Print a The item method is the default method for a collection object so we can omit it when we access an item in a collection. Removing an item: we can remove a specific member of a collection object either by position or by key. To remove an item from a collection we can use remove method. For example we want to remove 35 from Calcutta from the temp collection. Then we can do as follows. Syntax: object.remove(index) Example: temp.remove( Calcutta ) Counting a collection: the count is a return for number of items in the collection. Means to find out that how much items are in the collection. We can use the following statement. Temp.count Subroutine / Sub Procedure / Procedure: A sub procedure is a block of statement that are executed when it is invoked. Each time the procedure is called, the statement between sub and end sub are executed. Sub procedure are by default public in all module which means they can called from any where in the application so a subroutine / sub procedure is a block of statement that carries out a well defined task. Syntax of procedure. Public / Private / Static Sub procedurename(argument) End Sub In VB there are two type of sub procedure. 1. General procedure 2. Event procedure

13 Visual Basic 13 General procedure: Tells the application how to perform a specific task. Once a general procedure is define it must be specifically invoked by the application. A good programming is to put common statement in a separate procedure and have event procedure to call it. This eliminates the need to duplicate code and also make the application easier to maintain. General Procedure Example: Private Sub clear Text1.text = Text2.text = End Sub Event procedure: when an object (control) in VB recognize that an event has occur it automatically invoked the event procedure, It uses the name corresponding to the event, because the name established an association between the object and code event procedure are set to be attached to form and controls. Example: Private Sub Command_Click( ) Text2.text= End Sub An event procedure for a control combine the control actual name (specified in the name property) an underscore(_) and the event name. For instance if a command button named and play to invoke and event procedure when it is clicked we use the procedure: Cmd play_click() Function: like a sub procedure a function procedure that can take argument perform a series of statement and change a value of its argument unlike a sub procedure a function procedure can return a value to a calling procedure subroutine report anything to the calling program but function commonly carry out calculation & report the result: [static /public/private] function procedure (argument) [as type] statement Endsub Difference between subroutine & function: 1. We return a value by assigning it to the procedure name itself. When the function procedure return a value the value can them become part of a larger expression. 2. Generally, we call a function by including the function procedure name & arguments on the right side of larger statement or expression. 3. Function procedure have data type just have variable do, this determines the type of the return value.

14 Visual Basic 14 Control structure: Sometimes in programing we have to change flow of program. Some program needs conditions or decision making statements. Sometime we need repetition of statements. In both cases we should use control flow statements. For programming reason control flow statement change their sequence of execution in language. We can classify control statements in three types. 1. Conditional/ Selection Statement: In program we need to make decision to perform some calculation. These decision making statement are called conditional statement. VB supports 3 types of conditional statements. If then end if:- If statement is a powerful decision making statement. It is used to control flow of executing programming statements. In this statement if the given condition is true block of if will executed otherwise the next statement will be executed. If statement is one way selection statement and runs only if the condition is true. syntax:- If condition Then Statement line 1 Endif If then else end if: If else is a most usable conditional statement. This statement is also called two way selection statement in this statement if the condition is true first block of statement is executed otherwise second block of statement is executed if else statement is used in various forms such as simple if else, nested if else, if else ladder, we can write the syntax of statement as given below. If condition then Statement line1 Else Statement line2 End if Select case:- the select case structure compare one expression to different values VB provide the select case structure as an alternative to if then else or selectively executing one block of statement among multiple lock of statement. The advantage of the select case statement over multiple if then else statement as it makes the code easy or simple to read and maintain, when there are several choices. In select case structure check condition only one time and given the result according to it, means select case structure works with a single text expression, that is evaluated once at the top of the structure. VB compare then the result of this expression with the values for each case in the structure and if matches one of them the top of statement is processed.

15 Visual Basic 15 Select case test expression Case exp1 Statement 1 Case exp2 Statement 2 Case else Statement 3 End select Each expression list is a list of one are more values. If there is more then one value in single list the values are separate by comma. In the case else clause (which is optional). If none of the value in the expression list matches the text expression. Notice that the select case structure evaluates expression once at the top of the structure. In contrast the if then else structure can evaluate a different structure for each else if statement. We use select case structure only if when the if statement and each else if statement evaluates the same expression. 1. Repetitive or Looping Statement :- Sometimes in our program we need to repeat some statement to perform any calculation in this type of situation we use looping statements. The statement that enables us to execute asset of statement repeatedly till the required activity is completed called loops. This type of statement is also called the iterative statement. In VB starting of a loop and ending of loop are declared with keywords. VB support following looping statements. While wend loop:- the while wend loop execute a block of statement while a condition is true. If condition is true all statements are executed and when the wend statement is reached control is returned to the while statement which evaluates condition and if condition is true the process is repeated and if condition is false the program resumes with the statement. While condition Statement Increment/decrement Wend Example: Dim i% i=1 While(i<=10) Print i i=i+1 Wend Print terminate

16 Visual Basic 16 Do loop:- When VB executes do while loop it first test condition if condition is false it skip all the statements within do while loop and if condition is true VB execute the statement and goes back to the do while statement and test the condition again. Use a do loop to execute a block of statement. There are four types of do loop as given below. Do while condition Statement Increment/decrement Loop Example: Dim i% i=1 Do while(i<=10) Print i i = i + 1 Loop Print terminate Do loop while:- While VB execute this do loop while, the statement execute at least once because the condition is examined at end of the loop. After execute one time it checks the condition if it s true it execute all the statement and test the condition till then when it is true. Syntax of do loop while is as follows:- Do Statement Increment/decrement Loop while (condition) Example:- Dim i% i=10 Do Print i i=i+1 Loop while (i>11) Do until loop:- when VB execute this do until loop the statement execute if the condition is false and it check the condition again and again till then the condition is false. Syntax:- Do Until condition Statement Increment/decrement

17 Visual Basic 17 Loop Example:- Dim i% i=1 Do until(i>=11) Print i i=1+1 Loop Do loop until:- In it the statement execute at least once because the condition is examined at the end of the loop. After executing the statement one time. If condition is false or till then the condition is false, it execute the statement. Syntax Do Statement Increment/decrement Loop until condition Example:- Dim i% i=10 Do Print i i=i+1 Loop until (i<=11) For Next Loop:- We use a For...Next structure when we want to repeat a set of statements a set number of times. The syntax of a For..Next loop has three components: a counter, a range, and a step. When a For..Next loop is initialized, the counter is set to the first number in the range; The program then executes any code between the for and next statements normally. Upon reaching the next statement, the program returns to the for statement and increases the value of the counter by the step. To change the amount by which the counter variable increases on each iteration, simply change the value of the step. When the step is not explicitly stated, 1 is used by default. Note that the step can be a negative value. Syntax:- For counter [ As datatype ] = start To end [ Step step ] [ statements ] [ Continue For ] [ statements ] [ Exit For ]

18 Visual Basic 18 [ statements ] Next [ counter ] Example:- For i=1 to 10 Print i Next Exit:- The exit statement allows us exit directly from a for loop, do loop, sub procedure function procedure. The syntax for the exit statement is simple. Exit for and exit do can appear as many times as needed in the loop according. Exit for and exit do are useful where we required to quit a loop immediate without preforming any further statements with in the loop. Syntax:- For counter = start to end [step increment] Statements Exit for Statement Next [counter] Working With Forms: In VB, forms are container that make up the user interface when a VB application executing. The form is the top level object in VB application and every application start with the form. Form have a built in functionality that is always available without any programming apart. We can move a form resize it and even cover it with other forms with the mouse or keyboard. So in VB form is the medium of user interface in VB most of works depend on the form because the control and options available in VB can be place only on the form. So that they can accept values from user to complete the task. Loading And Unloading Forms: Load and unloads form use the load and unload statements. The load statement has following syntax: Load formname And the unload statement has the following syntax:- Unload formname The formname variable is the name of the form to be loaded or unloaded. The load statement does not show the form. We have to call the form show method to display it on the desktop. once a form is loaded it takes over the required resources so we should always unload a form that s not longer needed. When a form is unloaded, the resources it occupied are returned to the system and can be used by other forms or application if our application contain many forms, balance the benefit of having them all memory users loading certain forms as need it.

19 Visual Basic 19 Showing Form: To show a form we use the show method. If the form is loaded but invisible the show method brings the specified form on top of every other window on the desktop. If the form is not loaded the show methods it and then display it. The show method has following syntax:- formname.show [mode] For name variable is the form name and the optional argument mode, it can have one of the following value:- 0-modeless (default) 1-mode l Hiding Forms: If our application uses many forms. We may want to hide some of them. To hide a form use form s hide method whose syntax is form. Hide or to hide a form from with in its own code, use the following statement. Me.Hide. Forms that are hidden are not unloaded, they remain in memory and can be displayed with the show method. For example: form that may be opened frequently such as a search and replace window should be hidden when they are not needed when a form is hidden we can still access its property and code. Controlling The Form With In Another: In many situation we need of interaction between forms. Each form is design to operate independently of the other user interface. But they can communicate by globe or public variable. In other situation however we may need to control one form from with in another. Controlling the form means accessing its controls and setting or reading its values from with in another form code. Accessing a form s control from within another is straight forward simply prefix the control s name with the name of the form. For example:- to access text property of the text1 control on the form we should use following expression. Text1.Text To access to same property from within another form we would use this expression Form1.Text1.Text Form1 is the name of the form to which the text1 control belongs. We can actually have a text1 control on the form1 and in the expression text1.text Is the text property of the text1. So if we assign a string some text to the text1 control that is place on the form1 then we can use this code on the form1. Text1.Text = some text Now if we want to prime some string on form2 that is written in the text1 control of the form1 then we can use this code on form2. Print Form1.Text1.Text

20 Visual Basic 20 Text Box Control: The text box is the primary mechanism for displaying and entering text and is one of the most common element of the windows user interface. The text box control is small text editor that provides all the basic text editing facility that is inserting & selecting text scrolling. The text if it does not fit in the controls area. The text box is extremely versatile data entry tool that can be used for entering a single line of text such as a number or a password or for entering simple text files. Properties of text box: property determines appearance and functionality of text box. Text box have many properties, In which mainly used properties are as follows: 1. Multiline:- this property determines wheatear the text box control will hold a single line or multiple line of a text. By default. The control hold a single line of a text. To change the behavior set the multiline property true. 2. Max length:- this property determines the number characters the text box control will accepts. Its default value is zero. Which means the text may be of any length up to the controls capacity unit. 3. Password CHAR:- if we don t want to display the actual characters type by the user. Use this property to define the character to appear in place of each character the user types. The default value of the property is an empty string. It is necessary to use this property to set multiline property to false.for example :- if we set the value to an asterisk ( * ). The user sees an asterisk in the place of every character type. 4. Scroll bars:- this property controls the attachment of the scroll bar to the text box. Controls, if text exceeds the controls, dimensions single line text box can have a horizontal scroll bar. So that the user can view any part of a long line of text. If we attach a horizontal scroll bar to the text bar control. Multiline text boxes can have a horizontal or vertical scroll bar or both for manipulating the text. 5. Text property:- this property specifies the initial text that appears in the text box. A special cursor come play into with text and forms user end and edit text using the text cursor before we can use the text property. 6. Locked:- this property determines wheatear the user can enter value or change the default value of a text box. If this property is true. User can not change the text box value until at run time assign a false value to this property means this property makes a text box and only. 7. Alignment:- text box have a alignment property so we can set the alignment [ left (0), right (1), center (2)] of text box by this property. There are three possibilities by it:

21 Visual Basic Name:- to read or set the name of text box control this property can be used by default it is text 1, text2. And so on. Means this is the name of the control that can difference the control when we can do coding for that control. 9. Parent:- it is used to read the name of the form to which this belongs. This is mainly used in MDI form. 10. Visible:- it is use to set wheatear this control is visible or not. Events of text box control:- 1. Change:- to react a change in the text box control text property. 2. Click:- to react to the users clicked by mouse on this control. 3. Double click:- to react to the users double clicked by mouse on this control. 4. Drag drop:- to react to the user dragging another object over this control. 5. Get focus:- to initiate an action when this control receives the focus (cursor). 6. Last focus:- to initiate an action when this control losses the focus (cursor). 7. Key down:- to initiate an action when the user presses or hold a key down. 8. Key up:- to initiate an action when the user releases the key. 9. Key press:- to react to the users typing and ascci character. 10. Mouse down:- to react to the users pressing the mouse button. 11. Mouse move:- to react to users moving the mouse over this control. Manipulation text: 1. Text section:- the text box control provides three properties for manipulating the text selected by the user: a. Set text:- if we want to manipulate currently select text from with in our code, use the set text property. For example Clipboard. Set text(text1.settext) In the above example when we copy the text then the selected text copy in the clipboard. b. Set start and set length:- the set start property returns or sets the position of the first character of the selected text. Some what like placing the current in a specific location. And selecting text by dragging the mouse. The set length property returns or sets the length of the selected text. The most common use of these two properties is to extract the user selection or to select a peace of text with in the application. For example:- Text1.set start=0 Text1.set length=len(text1.text) In the above example we have done the coding of select all means when the user click on the select all button. The whole text return in the text box will be selected. The set start and set length properties always have a value if no text

22 Visual Basic 22 has been selected. In this case set length is zero and set start is the current location of the pointer in the text box. For text selection there is another property of the text box that is hide selection means when we select text in the text box control them if the hide election property is true then the text has select but it not shown as a selected text so that to get this task we must have to false wide selection property of text box. List Box And Combo Box Control: 1. List box:- a list box control occupies a user specified amount of space on the form and is populated with a list of items, the user can select one or more with the mouse. The items that can be displayed in the list box control must be inserted in the list box control through the code or by the list property in the properties window. Each new item in the list property must be entered in the new line, we can do this by using ctrl + enter, if we designing the items in the list at design time. 2. Combo box:- the combo box control also contain multiple item occupies less space on the screen. The combo box control is an expandable list box control. The user can expend it to make selection and retract it after the selection mode. The real advantage to the combo ox control however is that the user can enter new information in the combo box rather then being forced to select only the item listed. Basic Common Properties:- the list box and combo box controls provides a few common properties that can be set only at design time:- 1. Multi select (list box):- this property determines how the user can select list s items and must be set at design time. The multi select property value determines whether the user can select multiple items which method will be used for multiple selection. 2. Sorted:- in the list box control and combo box control if we want the items to be always sorted then we can set the controls sorted property to true. This property must be set at design and is read only at run time. Properties of list box control:- 1. Set control:- this property is used to read the number of selected items and this is run time property. For example:- msgbox (list1.set count) 2. List:- read or set the value of a listed item. 3. List count:- read the number of items in the list and it is only the run time property. 4. List index:- read or set index and the currently selected item in a list. It is only a run time property. If an item is not selected list box index is -1 and the first item in the list is list index zero.

23 Visual Basic 23 Methods of list box control:- 1. Add item:- to add item to the list box at the run time we can use the add item method its syntax is as follows:- list.additem (item, index) The item parameter is the string to be added to the list and index is its order. List1.addition( india ) List1.addition( Australia ) 2. Remove item:- to remove an item from a list we can use this method. We can also tell the index number to remove the item from the list box. Syntax:- List.remove item index Example: list1.remove item 0 3. Clear:- the clear method used to remove all the items from the control means this can remove all the contains of lit box control and make the list box empty. Example:- list1.clear 4. List() :- this is an array that holds the list s item. The element list (0) holds the first element of the list and list (1) holds the second item and so on up to list (list count -1) which holds the last item. Here is a program in which we can add all the items into list 2 from this list 1. Combo box properties:- 1. Style:- value_0:- this is the default value of combo box control. The control is mode up of a drop down list and a text box. 2. Value 1:- it include a text box and list that doesn t drop down. 3. Value -2:- this style is a drop down list frame which the user can select one of its items but can not enter a new one. Method of combo box:- Same list box Option Button: Option buttons, also called radio buttons, are typically used in a group of two or more. At any one time, only one button in the group can be "on". Clicking an option button turns it "on" and turns all other buttons in the group "off". Option button groups operate in a container control, such as a frame. Therefore, different sets of option button groups should be placed in their own frame on the form. If a group of option buttons is not contained within a frame, then the form itself acts as their container. In code, to perform an action based on which option button the user clicked, do one of two things: (1) To perform an action as soon as the user clicks an option button, place code in the Click event of the option button. (2) To perform a "delayed" action, such as when the user clicks a command button, check the Value property of the option buttons in the group. If the Value = True, then the button is "on".

24 Visual Basic 24 Examples using both methods follow. (Note: The examples in this topic use the builtin color constants vbred, vbgreen, and vbblue. First, a frame containing three option buttons, named optred, optgreen, and optblue respectively was placed on the form shown below: Next, code was written for the Click event of each of the option buttons. The code causes the background color of the form to change to the appropriate color when one of the option buttons is clicked: Private Sub optred_click() Form1.BackColor = vbred End Sub Private Sub optgreen_click() Form1.BackColor = vbgreen End Sub Private Sub optblue_click() Form1.BackColor = vbblue End Sub Check Box The checkbox acts as a "toggle" control: if it's on, clicking it turns it off; if it's off, clicking it turns it on. Unlike the option button, the operation of each checkbox on a form or frame is independent of all other checkboxes; changing the status of one does not affect other checkboxes. The program can read or set the status of a checkbox with the Value property (which is the default property of the checkbox). The Value property of a checkbox is of the Integer type. A value of 0 means "off", a value of 1 means "on". You can use the VB constants vbunchecked or vbchecked for 0 or 1, respectively. Scroll Bar: Scroll bar are most commonly used control. To control the up to down and left to right moment of a graphics and view or a list. So the scroll control is long strip with an indicator that lets the user select a value between two ends of the control, there are two types of scroll bar that are:- horizontal & vertical scroll bar. The horizontal scroll

25 Visual Basic 25 bar lets a user move left to right besides it the vertical scroll bar let s a user move up and down for a long document. To add a horizontal scroll bar we can use horizontal tool and to add a vertical tool bar we can use vertical tool. Properties of scroll bar control:- there are some main properties of scroll bar control that are as follows:- 1. Max:- this property is used to read or set the maximum value possible in a scroll bar. We can set this property at design time by using property window. And also set this property at run time by using the following. Code: Form-paint Hscroll1.max=100 Vscroll1.max= Min:- this is used to set the minimum possible value in scroll bar we can set this property at design by using the property window or at run time by using the following code: Form-paint Hscroll1.min=1 Vscroll1.min=1 3. Large change:- this is used to read or set the amount of change when a user clicks the bar, so the user clicks the scroll bar it self no the thumb (indigater) and no the arrow button.the thumb should move at direction by the amount set by the large change property we can set property at design time and also at run time. Form-paint Hscroll1.min=1 Hscroll1.max=100 Hscroll1.largechange=10 End sub 4. Small change:- this property use to read or set the amount of change when a user click on arrow the thumb move by an amount stored in the small change property. We can set this property also at design time and runtime. 5. Value:- this is used to read or set the current value of the control. The value property holds values that can be in the range spend by the value in the min and max property. We can set this value either design time or run time. Label1.caption=Hscroll.value Label2.caption=Vscroll.value

26 Visual Basic 26 Events of scroll box: 1. Change:- the change event occur every time changes the indicator position and release the mouse button. Means when the integrator being moved the change event is not occur and occur only when the mouse button released. 2. Scroll:- the scroll event occur continuously while the integrator is moving after the mouse button is released means with the scroll event we get continuous update at the action is happiness. Slider Control: Slider control is similar to scroll bar control but it does not cover a continuous range of values. The slider control has fixed number of tic. Marks which the developers can label. The slider control should be used when a user can type a numeric value and the value of our application accepted in a number in a specific range. The slider control icon does not appear in the tool box by default. To use the control in project we must right click the tool box and select component in the present menu and on the component dialog box check Microsoft common control 6.0. Properties of slider control: 1. Large change:- this property determines the number of ticks. And the default value of this property is five. We can set this property at design time and run time also. Slider1.largechange=5 Thus by this property the slider will move when the user press page up or page down key or click the mouse of either slider of current slider position. 2. Max:- this property is used to read or set the value of the last position. Its default value is ten. We can set this property at design time and also run time. Slider1.max= Min:- this property is use to read or set of the value of the first tic position. Its default value is zero and we can set this property at design time and also at run time. Slider1.min=1 4. Small change:- it determine number of ticks the slider will move when the user press right and left arrow key on keyboard. 5. Tick frequency:- it is used to determine the number of tick marks displayed on the control. Means to set the number of marks in a slider control we actually set the distance between ticks by using this property for example: If our slider scale goes from 0 to 100 A good for the slider tick frequency might be Tick style:- this determine the position of the tick- marks on the control. In fact we can place tick on one side. Both side or no sides of a slider. Here are some possible values of tick-style property. 1. Bottom right value 0

27 Visual Basic Top left value 1 3. Both value 2 4. No ticks value 3 7. Value property:- this is used to read or set the current value of slider control. We can get or set the value property at design time or run time. Slider1.max=250 Slider1.min=0 Slider1.largechange=10 Slider1.tickfrequency=25 Label1.caption=slider1.value Methods Of Slider Control: 1. Clear sel:- this is used to clear the current slider selection for example: slider1.clear sel 2. Get num ticks:- this is used to get the number of ticks in slider range. Events Of Slider Control: 1. Change:- we may use this event to catch the users slider section when the user is done moving the slider knob a change event occur. 2. Scroll:- the slider control also have scroll event to handle the continuous changes. List View Control An ImageList Control contains a collection of images that can be used by other Windows Common Control,Such as ListView, TreeView, TabStrip and ToolBar controls. It does not appeare on the form at run time. It serve as a container for icon that are accessed by other control such as ListView, Tree View, TabStrip and ToolBar controls. A ListView control displays data as ListItem objects. each ListItem object can have an optional icon associated with the Label of the object. Tree View Control: The TreeView control display a hirearchical display node object.each node consist of label,optional bitmap.you use this control to display the information in hierarchical tree. The TreeView control is designed to display data that is hierarchical in nature, such as organization trees, the entries in an index, the files and directories on a disk. Uses of TreeView To create an organization tree that can be manipulated by the user. To create a tree that shows at least two or more levels of a database.

28 Visual Basic 28 Unit IV SDI or MDI Interface: Two different styles are available for the Visual Basic IDE: Single Document Interface(SDI) or Multiple Document Interface(MDI). ABOUT SDI Most applications use a Single Document Interface. Each window of the application holds a single document, so if the user wants to open more documents with that application, he must open a new window. It's also the default mode when building an application with Visual Basic. Windows Notepad is an example of a typical SDI application. ABOUT MDI Multiple Document Interfaces were popular in versions of Windows prior to Windows 95, but they've become less common. With an MDI, each window within an application holds multiple documents, usually in sub-windows. New documents open within the existing window and the information is shared with all other open documents. MDI applications include tabbed Web browsers, such as Mozilla Firefox, where users have the option to open documents in multiple tabs within the same window. ADVANTAGES OF SDI An SDI interface works very well with multiple monitors and multiple virtual desktops. It also allows users to switch between multiple open documents using the native Windows taskbar and task manager, rather than through special code that you would need to write into your application. ADVANTAGES OF MDI MDI applications can often handle multiple documents more readily than SDI programs. For example, many MDI text editors allow the user to open multiple text files side by side in the same window, making it easy to compare and look up information from a second document while working on the first. STABILITY AND PERFORMANCE SDI applications tend to be more robust and bug-free than MDI applications, since a serious error with one document rarely affects the other documents within an SDI environment. For example, if one Windows Notepad document crashes, any other open copies of Notepad will usually survive the crash. On the other hand, if one Web page in Firefox causes the browser to crash, all the open Web pages die with it. Nevertheless, MDI applications tend to perform more quickly than SDI programs, since only one version of the application is loaded into memory. MDI (multiple document interface): The MDI was designed to simply the exchange of information among document are under the same roof. With an MDI application we can maintain multiple open window but not multiple copies of the application. In VB we can develop MDI applications easily in which the main form or MDI form is not duplicated but it acts as a container

29 Visual Basic 29 for all other windows and its call the parent window windows in which the individual document are displayed are called child window. When we are position the parent window on the desktop its child window follow it. And MDI application must have at least two forms. Parent or one or more child forms, each of these form has certain properties:- there can be many child form contented with in the parent form but there can be only one form. The parent form may not contain any control except child form but it has its own menu. To create an MDI application we can follow these steps:- 1. Start a new project and then choose project -> add MDI form, to add the parent form. 2. Set the forms caption to MDI window. 3. Choose project -> add form to add a regular form. 4. Make this form the child form by setting its MDI child property to true. To donate that this is a child form. VB automatically associate this new form with the parent form: Menus: Menus group command into categories which describe the type of commands a menu contains. A menu bar normally appear directly beneath the title bar of a window and list the title of the menus. The commands of each menu in the menu bar display below menu title when it is selected. In VB menus are created using the menu editor which is a dialog box. Sub menus and separate bars are also created with the menu editor. Each item in a menu is a object which means that the properties of all set using the properties window. Designing menus:- we use menu editor to create menus in VB so that to open the menu editor open a form in the form window and then choose menu editor from the tools menu or press ctrl+e. The top level of the menu is the title displayed in the menu bar like edit, view etc. are some of the most commonly used menu titles. To add to our own menu we can follow these steps. 1. Open the menu editor by selecting menu editor from tools menu or by pressing ctrl+e. 2. Enter & file in the caption text box (adding an ampersand before a letter makes that letter the access key for item) 3. Enter menu file into the name text box that is the name that can be used or difference the menu when we will do coding for that menu. 4. Click the next button. 5. Repeat steps 1 through four for creating next menu like edit view etc. and change the caption and name text box accordingly. Click the ok button to accept the menu structure that we have created and return to the form window.

30 Visual Basic 30 Designing sub command and menu:- menu item must be added to the next level of the menu structure. These item appears commands in the menu of the title in the label immediately above them. To add commands to the menu the steps are as follows. 1. Open the form from the previous section in the form window. 2. Open the menu editor. 3. Select the edit menu from the list box at the bottom of the dialog box. 4. Click the insert button this insert a menu item before the one that is currently selected. 5. Click the right arrow button to make this item one level below the menu item above it. 6. Repeat these step for each menu item to add a menu and click on the ok button. PopUp Menu Or Shortcut Menus:- shortcut menus appears when user click the right mouse button. The contest of the shortcut menu depends upon the context in which it was opened. For example:- right click on a text box should open a shortcut menu that deals with text but the same menu doesn t make sends to appear. If right clicking on a graph display. VB provides a method for opening this pop up menu or shortcut menu. Only one pop up menu can be open at any time. Object pop up menu menuname flag, x, y, bold command The object argument is optional for this method it refer to a form but if omitted VB just uses the form that has the focus at the time. Menu name can be any menu item that has at least one sub menu item in the level directly below it. Flags is a parameter that effects appearances and behavior of the pop up menu. The x, y argument specify the location at which the menus display. The bold command argument specifies a menu item to appear in bold. Only one item can appear bold at any one time. Dialog Box: Dialog is general term a discussion between two or more people it allows one user to interacts with other. This lead to the development of dialog box in VB. Two types of dialog box exists and they are model and modeless. VB provides a number of pre defined dialog boxes and they accept parameters use to customize these behavior and appearances. Message box:- the message box display a dialog box that is created using the argument supplied to it. This is a simple dialog box that display a message and accepts feedback from users only through the form of closing the dialog box. The user can enter no text, means user has no choice but to press the ok button to close this dialog box. Because there is only one way to close this dialog box. Syntax:- msg box (prompt[button] [title] [help file, context]) The prompt is the only argument that is required for msgbox functions. It is a screen that is display in the message area in the dialog box. All other parameters are

31 Visual Basic 31 optional we can also interact the user by changes the optional button parameters in our application that is :- Vbok 1. Ok Vb cancel 2. Cancel Vb abort 3. Abort Vb retry 4. Retry Vb ignore 5. Ignore Vb yes 6. Yes Vb no 7 no Here is a simple msgbox that present a message and ok button using the message function. Msg box( message loaded ) Input Box:- to give the user ability to supply any value that they wish, we can use the input box. Syntax is as follows:- Input box(prompt [title] [default], [xpos], [ypos], [helpline, context]) The prompt and title argument has the same effect as they have in the msg box like prompt is use to display any information and title is use to display something in title bar of input box and is required if the default value is supplies to the input box function, It appears in the text box of the dialog box If omitting (skip) the default value then it leaves the text box blank. And x and y position for the location of the dialog box on the screen is supplied using the xpos and ypox argument which accepts the distance of the edge of the dialog box from the left and the top of the screen respectively leaving out xpos centers the dialog box horizontally while leaving out ypos place the dialog box about one third of the way from the top of the screen.

32 Visual Basic 32 Common Dialog Box Control: The common dialog control provides an easy way to produce standard dialog boxes. The common dialog box can display file different dialog boxes. 1. Open a file 2. Save a file 3. Set a color 4. Set a font 5. Print a document Common dialog control is not on the tool box, we can follow these steps to make available it on the tool box. Right click on the tool box or select component s from project menu. Check the micro-soft common dialog control 6.0 option and click on ok. After the control is placed on the form we can not abject its size because common dialog control remains hide at run time and it has not size property. Methods Of Common Dialog Box Control:- 1. Show open:- it is used to display the open common dialog box. 2. Show save:- to display the save as common dialog box. 3. Show color:- to display the color open dialog box. 4. Show font:- to display the font display box. 5. Show printer:- to display the printer common dialog box. 6. Show help:- to display the help dialog box. Properties Of Common Dialog Box Control:- 1. Cancel error:- if an error is generator when user clicks on the cancel error button then to handle error set the cancel error property to true. 2. Dialog title:- this property sets the string displays in the title bar of dialog box. 3. Flags:- flags used to abject the function of each common dialog box the value of this property will very depending on the specific common dialog box being opened. Means it is used to change various elements on the dialog box. 4. Min & max:- in print dialog box this property determine the minimum and maximum values for the print range that the user can specify in the font common dialog box this property determine the minimum and maximum size displayed in the size list. 5. Color: this is use to read or set selected color. 6. File name:- this is used to read or set the path and name of the file to open and save. 7. Filter:- this property returns or set the filters that the displayed in the type list box of a dialog box means this property displays only certain type of files.

33 Visual Basic 33 File Open Dialog Box:- This dialog box offers a standard interface for users when they select a file to open the dialog box. Handle the folder and network selections. This dialog box has four options which determine what appear in the save as type box. 1. Filter index:- if we want to use a filter value then we can use the filter index property to determine which filter will be displayed as default when the open or save dialog box will open. 2. File title:- this returns the name of the file to be opened or save. The file title property does not include the path name. 3. In it DIR:- this sets the initial directory in which files are displayed the first time when the open and save dialog box are opened or we can also specify the folder in which the application will store its file by default. 4. Max file size:- this return or set the maximum size of file name opened use in the common dialog control. File Save Dialog Box: This is virtually identical to the file open dialog box except for the title and a few other options such as the command button titles, like in file open dialog box the open command button is known as save command button in file save dialog box Same four point Color Dialog Box: A color dialog box provides a simple way for users to specify color value. We display the dialog box with a common dialog method show color and also follows three steps:- 1. Set the common dialog box control dialog title property to the title we want to appear in color selection title bar such as select a back ground color. 2. Set the common dialog box control flag property if we want to set one of flags. 3. Trigger the font selection dialog box display by applying the show font method to the common dialog box in coding. Possible values of flag property: 1. Set the initial color. 2. Display the entire dialog box including the define custom color. 3. Prevent users for defining customs color. 4. Display help button in dialog box. The Font Dialog Box: It is used to display the dialog box by using which we can change the style of our font. We don t know exactly which font of our application PC will contain. The common dialog box control font dialog box search the user s. All the font in the

34 Visual Basic 34 computer and display those font inside the font dialog box. For search the fonts in the user system we set or use the flag property. The possible values are as follow:- 1. CDLCF screen font:- show screen fonts. 2. CDLCF printer fonts:- show printer font. 3. CDLCF both:- show both type of font. We use common dialog control show font method to show a font dialog box But before we use the show font method we set the flag property of it. The attributes of the selected font we presented through the following property. 1. Color 2. Font bold 3. Font italic 4. Font underline 5. Font strikethrough 6. Font name For set the color, font strikethrough and font underline property we must first select the flag property to CDLCF effects. Print Dialog Box: When we apply the show printer to a common dialog control we can set the select printer type, number of copies, range of pages and several other printing options. Our print dialog will very depending on our printer type. Help Dialog Box: We can display a windows help fill with the common dialog control show help method. To use this method we first sets the common dialog control help command property. The basic properties of help dialog box are as follows:- 1. Help file:- the file name of windows help file that will be use to display online help 2. Help command:- this constant listed in the table look like flags but they are actually parameters the help command property. 3. Help context ID:- this id is a number that tells where is the help file and it will find the pages describing the specific topic. 4. Help key:- the keyword that identifies the requests help topic. Text Box Control (Selection, Search, Replace):

35 Visual Basic 35 Graphics In VB: Graphics forms a very important part of visual basic programming because an attractive user interface will be appealing to the users. There are four basic controls in VB6 that we can use to draw graphics on our form: the line control, the shape control, the image box and the picture box. Before we draw anything, we must know the dimensions of the control we are about to draw on and the units it uses. To do this, we must understand coordinates and coordinate systems and how they are used in drawing. Coordinate system: coordinates describe the position of the individual pixels on the screen or of. the points on a piece of paper in the printer. The coordinate system is similar to ) a city map. Each square on the map has its own unique address: a combination of a column: and a row number. The column number is the vertical coordinate, or Y coordinate. The row number is the horizontal coordinate, Or X coordinate. Any point on the Form can be identified by its X and Y coordinates, andwe refer to it as the point at coordinates (X,Y) or simply the point (X, Y). An example is shown in Figure. The values along the x-axis in the coordinate system of the figure go from 0 to 100, and the values along the y-axis go from -so to so. Any pair of numbers in the ranges 0 to 100 and ~SO to SO specifies a point on the Form. The point with the smallest coordinates is the origin of the coordinate system. In Visual &Sic, the origin of the coordinate system is the upper-left comer of the control or Form. The X coordinates increase to the right and the Y coordinates increase downward. Each coordinate is a number and it may or may not correspond to a meaningful unit. Visual Basic s default coordinate system uses a unit called iunp, which equals 1/20 of a point. A point is a typographical measure of unit; there are 72 points in an inch and 1,440 twips in an inch. The twip is a precise unit of measurement, probably more precise than we need today. It does, however, allow us to draw shapes that will look good even when printed on a 1,200 dpi laser printer. But because twips aren t convenient in all situations, Visual Basic provides the eight coordinate systems

36 Visual Basic 36 To change the default coordinate system, assign the appropriate value to the ScaleMode property. If you set ScaleMode to Inches; distances on the control must be specified in inches. In tlus case, two points that are one unit apart are one inch from each other. You can also specify decimal distances such as 0.1, which corresponds to 1/10 of an inch. l hanging the ScaleMode property doesn t resize or otherwise affect the control. It simply changes the density of the grid you use to address the points on the control. The line and Shape controls: To draw a straight line, just click on the line control and then use your mouse to draw the line on the form. After drawing the line, you can then change its color, width and style using the BorderColor, BorderWidth and BorderStyle properties. Similarly, to draw a shape, just click on the shape control and draw the shape on the form. The default shape is a rectangle, with the default shape property set at 0. You can change the shape to square, oval, circle and rounded rectangle by changing the shape property s value to 1, 2, 3, 4, and 5 respectively. In addition, you can change its background color using the BackColor property, its border style using the BorderStyle property, its border color using the BorderColor property as well its border width using the BorderWidth property. PSet, Line and Circle Drawing Methods Other than using the line and shape controls to draw graphics on the form, we can also use the Pset, Line and Circle methods to draw graphics on the form. (a) The Pset Method The Pset method draw a dot on the screen, it takes the syntax Pset (x, y ), color (x,y) is the coordinates of the point and color is its color. To specify the color, we can use the color codes or the standard VB color constant such as VbRed, VbBlue, VbGeen and etc. For example, Pset(100,200), VbRed will display a red dot at the (100,200) coordinates. The Pset method can also be used to draw a straight line on the form. The procedure is For x= a to b Pset(x,x) Next x This procedure will draw a line starting from the point (a,a) and to the point (b,b). For example, the following procedure will draw a magenta line from the point (0,0) to the point (1000,1000). For x= 0 to 100 Pset(x,x), vbmagenta Next x

37 Visual Basic 37 (b) The Line Method Although the Pset method can be used to draw a straight line on the form, it is a little slow. It is better to use the Line method if you want to draw a straight line faster. The format of the Line command is shown below. It draws a line from the point (x1, y1) to the point (x2, y2) and the color constant will determine the color of the line. Line (x1, y1)-(x2, y2), color For example, the following command will draw a red line from the point (0, 0) to the point (1000, 2000). Line (0, 0)-(1000, 2000), VbRed The Line method can also be used to draw a rectangle. The syntax is Line (x1-y1)-(x2, y2), color, B The four corners of the rectangle are (x1-y1), (x2-y1), (x1-y2) and (x2, y2) Another variation of the Line method is to fill the rectangle with a certain color. The syntax is. Line (x1, y1)-(x2, y2), color, BF If you wish to draw the graphics in a picture box, you can use the following syntaxes Picture1.Line (x1, y1)-(x2, y2), color Picture1.Line (x1-y1)-(x2, y2), color, B Picture1.Line (x1-y1)-(x2, y2), color, BF Picture1.Circle (x1, y1), radius, color (c) The Circle Method The circle method takes the following syntax Circle (x1, y1), radius, color That draws a circle centered at (x1, y1), with a certain radius and a certain border color. For example, the procedure Circle (400, 400), 500, VbRed draws a circle centered at (400, 400) with a radius of 500 twips and a red border. Image Box & Picture Box Picture Box and Image controls are used to display images, But there are some differences between the two controls. There are certain cases when the Image control is suitable, and in some other, the PictureBox control will make our task easier, though both of them share the same job. So lets dig into some details! Where to use images? The first plain fact to know is that the Image and PictureBox controls are used to display pictures or icons on the form. We generally use pictures or icons for the company logo and to make your software more graphical that'll surely make our application user-friendly. We can make use of the images on the splash screen and in many other cases. The supported picture formats for these control include BMP, DIB (bitmap), ICO (icon), CUR (cursor), WMF (metafile), EMF (enhanced metafile), GIF and JPEG.We can't use a PNG format. Firstly we'll talk about the PictureBox control and then the Image control. Lastly the comparison and differentiation between them will be discussed along with the explanation of when to use one or another.

38 Visual Basic 38 The PictureBox control The following points describe a PictureBox control: The picturebox control comes with a light border around it. Works as a container: we can place any other control on it, when we move the PictureBox control, all the controls on it moves along with. That means, it works as a container of other controls. Similarity with the Form: This control is so similar to a form as both of them support all the graphical properties, graphical methods and conversion methods. Supports all the graphical properties: It supports all the graphical properties such as AutoRedraw, ClipControls, HasDC, FontTransparent, CurrentX, CurrentY, and the Drawxxxx, Fillxxxx, and Scalexxxx properties. Supports all the graphical methods: It supports all the graphical methods such as Cls, PSet, Point, Line, and Circle. Supports the conversion methods: It supports the conversion methods such as ScaleX, ScaleY, TextWidth, and TextHeight. Loading images: Using the Picture property, we can load a picture in design time and run-time. The LoadPicture function is used to load the picture from our computer. This function is used with both the PictureBox and Image controls. Example: Picture1.Picture = LoadPicture("D:\\PictureName.jpg") Example: Image1.Picture = LoadPicture("D:\\PictureName.jpg") Clearing the current image: we can clear the current image of the PictureBox or Image control in design time by clearing the value of Picture property. This can also be done in run-time in the following way. Picture1.Picture=LoadPicture("") or set Picture1.picture=Nothing The Image Control The image control has almost the same features of PictureBox. Loading Images: we load an image in the same way. Example: Image1.Picture = LoadPicture("D:\\PictureName.jpg") The Stretch property: If you set the Stretch property to true, it stretches the picture to fit in the control. Difference between Image control & PictureBox. 1. Image controls are less complex than PictureBox controls. 2. The Image control does not have border around it like a PictureBox control. 3. The image control does not work as a container. 4. The Image controls do not have graphical properties, graphical methods or conversion methods such as ScaleX, ScaleY, TextWidth, and TextHeight. 5. The PictureBox control does not have the Stretch property. 6. The Image control comparatively takes less memory, so it loads faster.

39 Visual Basic 39 Conclusion As a conclusion I want to say that many Visual Basic programmers prefer the Image control over PictureBox as the Image control consumes less memory resource resulting a faster loading of it. Besides, it supports all the events a picturebox can have, and you can even have a border around it from the BorderStyle property. The only big limitation is that it cannot work as a container. For this reason, the PictureBox control can be sometimes preferred much. But above all, we should always choose one which is appropriate for our application. DLL A dynamic link library (DLL) is a library of functions and procedures that can be called from an application or another DLL. Using a library in this way has two major functions: It permits the sharing of code. The same DLL can be used by many other DLLs and applications. The Win32 API, for instance, is implemented as a series of Windows DLLs. Moreover, as long as multiple processes load the same DLL at the same base address, they can share the code in the DLL. In other words, a single DLL in memory can be accessed by multiple processes. It allows for component-based and modular development, which makes development and the upgrade process easier. Ordinarily, when a static library is used in application development, the library's modules must be linked into the finished application. With dynamic linking, the modules reside in a separate DLL file that is loaded dynamically, either when the application loads or when its member functions are needed. A dynamic link library may include internal functions, which can be called only from within the DLL. Its main purpose, however, is to provide exported functions-- that is, functions that reside in a module of the DLL and can be called from other DLLs and applications. Frequently, a definition (.def) file is used in C/C++ projects to list a DLL's exports. A DLL also includes an optional entry point, which is called when a process or thread loads or unloads the DLL. Windows calls this entry point when a process loads and unloads the DLL. It also calls the entry point when the process creates or terminates a thread. That allows the DLL to perform any per-process and perapplication initialization and cleanup.

40 Visual Basic 40 UNIT V Recursive Procedures: A recursive procedure is one that calls itself. In general, this is not the most effective way to write Visual Basic code. The following procedure uses recursion to calculate the factorial of its original argument. Function factorial(byval n As Integer) As Integer If n <= 1 Then Return 1 Else Return factorial(n - 1) * n End If End Function Considerations with Recursive Procedures Limiting Conditions. we must design a recursive procedure to test for at least one condition that can terminate the recursion, and we must also handle the case where no such condition is satisfied within a reasonable number of recursive calls. Without at least one condition that can be met without fail, our procedure runs a high risk of executing in an infinite loop. Memory Usage. our application has a limited amount of space for local variables. Each time a procedure calls itself, it uses more of that space for additional copies of its local variables. If this process continues indefinitely, it eventually causes astackoverflowexception error. Efficiency. we can almost always substitute a loop for recursion. A loop does not have the overhead of passing arguments, initializing additional storage, and returning values. Our performance can be much better without recursive calls. Mutual Recursion. we might observe very poor performance, or even an infinite loop, if two procedures call each other. Such a design presents the same problems as a single recursive procedure, but can be harder to detect and debug. Calling with Parentheses. When a Function procedure calls itself recursively, we must follow the procedure name with parentheses, even if there is no argument list. Otherwise, the function name is taken as representing the return value of the function. Testing. If we write a recursive procedure, we should test it very carefully to make sure it always meets some limiting condition. We should also ensure that we cannot run out of memory due to having too many recursive calls.

41 Visual Basic 41 Testing and Debugging: Visual Basic has built in Error Scanning to check for syntax errors. For example, if you forget to put the "Then" keyword at the end of an If statement, you get an error message saying, "Expected: Then or GoTo". TYPES OF ERRORS: There are three types of error that can occur: 1. Compile-Time. 2. Run-Time 3. Logical. Visual Basic's error scanning only detects errors made on a single line. A missing "End If" is an example of a compile-time error, and would be detected when the program is compiled before a run. Errors can also arise during the execution of a program and are called run-time errors. An example of a run-time error might be the wrong data type provided for a field in a database or trying to divide by zero. Logical errors are the hardest to detect as they follow the rules of the programming language, but behave in a manner that was not intended. Logical errors occur through incorrect logic such as using a logical "And" instead of a logical "Or" in a condition. VISUAL BASIC DEBUGGER: Make sure the Debug toolbar is visible by putting a check against "Debug" in the "View", "Toolbars" menu item. When the program is running, you can pause it so you can examine values or set test value by pressing the "Break" button on the toolbar. INTERMEDIATE PANE You can examine variables directly in the Intermediate Pane with the Print command, and set values with the assignment operator. Typing, Print Me.Left would return the left position of the form, and typing me.left = 1000 would set the left position of the form to You can also print to the Intermediate Pane from Visual basic with the Debug object's Print method. Debug.Print Me.ScaleWidth - shpball.left + shpball.width The Debug object's Assert method may be used to enter "Break Mode" should condition not be true. The following will go into Break Mode if a Shape is positioned outside the right hand side of the Form. Debug.Assert shpball.left + shpball.width & Me.ScaleWidth Breakpoints and Watches are two useful features of the debugger, that allow you to halt the program at a certain point or observe variables to track the logic. BREAKPOINT The Toggle Breakpoint command is used to add/remove breakpoints where the cursor is positioned in the code window. Breakpoints cause the program to enter "Break Mode", and display the block of code on screen in order you may examine values and step through the code. Breakpoints may also be added by clicking on the "Margin Indicator Bar" on the left of the code window.

42 Visual Basic 42 STEPPING THROUGH THE CODE The Debug Step commands allow you to step through the program in order to visually trace the flow of execution. The Step Into command executes the current statement. If the current statement is a procedure or function, the next statement will be the first line of the procedure or function. The Step Over command executes the current statement. If the current statement is a procedure or function, the procedure or function is executed as a single statement. The Step Out command executes the remaining statements in a procedure or function. THE LOCALS WINDOWS: The Locals Window displays the value and data types of all variables in the module or form. You can also inspect the state of the Form's properties with the "Me" entry. THE WATCH WINDOW: Variables are add to the watch window by either right-clicking the variable and selecting "Add Watch" or by selecting "Add Watch" from the "Debug" menu. "Break When Value Is True" causes the program to enter "Break Mode", should the value be True, and Break When Value Changes causes the program to enter "Break Mode" whenever the value changes. QUICK WATCH: Variables may be added to the watch window by highlighting the variable and selecting "Quick Watch" from the "Debug" menu. Clicking "Add", adds the variable to the Watch window. CALL STACK The Call Stack window allows you to see the list of procedures that were called in order to get to the current statement. The window may either be displayed by selecting "Call Stack" from the "View" menu or by clicking the "Locals" window's "Call Stack" button. ERROR TRAPPING The On Error statement is used to trap errors in Visual Basic 6. VB.Net uses the Try, Catch methods in order to eliminate the need for a GoTo statement. The On Error command must be placed in the procedure at a position before the error could arise. The "Exit Sub" statement is used before the error handling part in order to avoid running the error handling code when there is no error. The Error object is built-in with global scope and contains the state of errors that may have occurred.the Number property provides the error number, and the Description property is a translation of the error. Private Sub drvlist_change() On Error GoTo driveerror dirlist.path = drvlist.drive Exit Sub driveerror: MsgBox Err.Description, vbexclamation, "Drive Error" End Sub

43 Visual Basic 43 THE RESUME STATEMENT The Resume statement is used to specify where to restart the flow of execution. This can either be a label, or Next. If Next is used, execution is continued from the statement following the statement that caused the error. The following example prompts the user what to do should a drive error occur using the, Resume Next statement. Private Sub drvlist_change( ) On Error GoTo driveerror retrydrive: dirlist.path = drvlist.drive Exit Sub driveerror: Dim response As Integer, description As Integer description = vbexclamation + vbretrycancel response = MsgBox(Err.Description, description, "Drive Error") If response = vbretry Then Resume retrydrive End If End Sub On Error Resume Next, skips any run-time errors that may occur. On Error GoTo 0, turns error trapping off. The following example ignores errors. Private Sub drvlist_change() On Error Resume Next dirlist.path = drvlist.drive End Sub RAISING AN ERROR The Raise method of the Err object may be used to rethrow the error. This is particularly useful with class modules, as you can specify the source and a description of the problem. description = "Unable to process the data provided" Err.Raise Err.Number, "myobject", description The following example handles all errors returned from the InputBox, except incorrect data types (Error code 13). Dim age As Integer On Error GoTo incorrectdatatype age = InputBox("Enter your name", "Age") Me.Print "You are " & age & " years old" Exit Sub incorrectdatatype: If Err.Number = 13 Then Err.Raise 13 Else MsgBox Err.description, vbexclamation, "Error" End If

44 Visual Basic 44 Database programming: Connecting to an Access Database Using the VB Data Control STEPS: 1. Open a new Visual Basic project. 2. Put a data control (an intrinsic control, located in the VB toolbox) on the form and set the properties as follows: Property Value (Name) datauthors Caption Use the arrows to view the data Connect Access (default) DatabaseName..\biblio.mdb DefaultType UseJet (default) RecordSource Authors (choose from list) Notes: When you use the Data Control in a project, the properties that must be set are DatabaseName and RecordSource, in that order. DatabaseName is the name of the database you want to use, and the RecordSource is the name of the table in that database that you want to use. On your form, create a text box for each field in the Authors table, with labels. (If you were to open the database in Access, you would see that the three fields of the Authors table are Au_ID, Author, and Year Born.) Set the properties of the three textboxes as follows: Name DataSource DataField txtauthid datauthors Au_ID txtauthor datauthors Author txtyearborn datauthors Year Born In addition, set the Enabled property of txtauthid to False. When you want a control (such as a text box) to display data from a database, the properties that must be set are DataSourceand Datafield. The DataSource is the name of the data control on the form (it should already be configured), and the DataFieldis the name of the particular field in the database that should be displayed in the control (this field will be in the table that was chosen for the RecordSource of the data control). At this point, your form should resemble the screen-shot below:

45 Visual Basic Save and run the project. Use the arrows on the data control to scroll through the data. 5. On any record, change the data in the author name or year born field. Move ahead, then move back to the record you changed. Note that your changes remain in effect. The data control automatically updates a record when you move off of the record. Note that this exercise demonstrated that you can create a simple but functional application that allows the user to browse through the rows of a database table (or result set) and to update rows in that table without writing any code.

46 Visual Basic 46 The following example will illustrate how to build a relatively powerful database application using ADO data control. It is in fact a library application. First of all, name the new form as frmbooktitle and change its caption to Book Titles- ADO Application. Secondly, insert the ADO data control and name it as adobooks and change its caption to book. Next, insert the necessary labels, text boxes and command buttons. The runtime interface of this program is shown in Figure 25.1 below, it allows adding and deletion as well as updating and browsing of data. Figure 25.1: The Runtime Interface The property settings of all the controls are listed as in Table 25.1 below: Table 25.1: Property Settings Control Property Setting Form Name frmbooktitle Form Caption Book Titles - ADOApplication ADO Name Label1 Name adobooks lblapp Label1 Caption Book Titles Label 2 Name lbltitle

47 Visual Basic 47 Label2 Caption Title : Label3 Name Label3 Caption Label4 Name Label4 Caption Labe5 Name Label5 Caption Label6 Name lblyear Year Published: lblisbn ISBN: lblpubid Publisher's ID: lblsubject Label6 Caption Subject : TextBox1 Name TextBox1 DataField TextBox1 DataSource TextBox2 Name TextBox2 DataField TextBox2 DataSource TextBox3 Name TextBox3 DataField TextBox3 DataSource txtitle Title adobooks txtpub Year Published adobooks txtisbn ISBN adobooks

48 Visual Basic 48 TextBox4 Name TextBox4 DataField TextBox4 DataSource TextBox5 Name TextBox5 DataField TextBox5 DataSource Command Button1 Name Command Button1 Caption Command Button2 Name Command Button2 Caption Command Button3 Name Command Button3 Caption Command Button4 Name Command Button4 Caption Command Button5 Name Command Button5 Caption Command Button6 Name Command Button6 Caption txtpubid PubID adobooks txtsubject Subject adobooks cmdsave &Save cmdadd &Add cmddelete &Delete cmdcancel &Cancel cmdprev &< cmdnext &>

49 Visual Basic 49 Command Button7 Name Command Button7 Caption cmdexit E&xit To be able to access and manage a database, you need to connect the ADO data control to a database file. We are going to use BIBLIO.MDB that comes with VB6. To connect ADO to this database file, follow the steps below: a) Click on the ADO control on the form and open up the properties window. b) Click on the ConnectionString property, the Property Pages dialog box will appear, as shown in Figure Figure : Property Pages When the dialog box appear, select the Use Connection String's Option. Next, click build and at the Data Link dialog box, double-click the option labeledmicrosoft Jet 3.51 OLE DB provider.

50 Visual Basic 50 Figure : Data Link Properties After that, click the Next button to select the file BIBLO.MDB. You can click on Text Connection to ensure proper connection of the database file. Click OK to finish the connection. Finally, click on the RecordSource property and set the command type to adcmd Table and Table name to Titles. Now you are ready to use the database file.

51 Visual Basic 51 Figure 25.4 Now, you need to write code for all the command buttons. After which, you can make the ADO control invisible. For the Save button, the program codes are as follow: Private Sub cmdsave_click() adobooks.recordset.fields("title") = txttitle.text adobooks.recordset.fields("year Published") = txtpub.text adobooks.recordset.fields("isbn") = txtisbn.text adobooks.recordset.fields("pubid") = txtpubid.text adobooks.recordset.fields("subject") = txtsubject.text adobooks.recordset.update End Sub For the Add button, the program codes are as follow: Private Sub cmdadd_click() adobooks.recordset.addnew End Sub For the Delete button, the program codes are as follow: Private Sub cmddelete_click() Confirm = MsgBox("Are you sure you want to delete this record?", vbyesno, "Deletion Confirmation") If Confirm = vbyes Then adobooks.recordset.delete MsgBox "Record Deleted!",, "Message" Else MsgBox "Record Not Deleted!",, "Message" End If End Sub For the Cancel button, the program codes are as follow: Private Sub cmdcancel_click() txttitle.text = "" txtpub.text = "" txtpubid.text = "" txtisbn.text = "" txtsubject.text = "" End Sub