Visual BASIC Creating an Application. Choose File New Project from the menu

Transcription

1 Creating an Application Choose File New Project from the menu Choose Windows Application Name the project Copyright Project Place a check in the Create directory for solution box Click Browse Choose and/or create the folder to store the project in Click OK to save it 1

2 The Visual BASIC project screen appears Auto-hide Button Project Name and Information Windows Form Designer Window Property Window The Auto-hide Button causes the Solution Explorer window to minimize to a tab Pointing to the tab makes the window reappear 2

3 The Auto-hide button is then sideways Clicking it again makes the window appear again and toggles the auto-hide off. Clicking the Start Page tab to see it Click the Close Button to close it 3

4 Choosing the Reset Window Layout option from the Window menu option will cause the window to appear as it did when opened Clicking the Data Sources tab shows that window Clicking the Close Button will close that window 4

5 The Windows Form Designer Window Name of disk file containing the Form object Title Bar Windows Form object Windows Solution Explorer Window Show All Files Button Form file containing the code 5

6 The Properties Window Categorize Button Shows properties by category Alphabetize Button Shows properties in alphabetical order Object box Settings box Properties List Description Pane An object s properties will become visible in the Properties Window when the object is chosen in the Solution Explorer Window. Changing an Object s Property Place the insertion point in the property value and retype the new property (Here, we changed the name of the form to Copyright Form1.vb) The changes are reflected in the Solution Explorer Window as well 6

7 Properties of the Windows Form Object Name of Windows Form object Location of the Form class Class Name To see the properties of the Windows Form object, click on it in the Windows Designer Window. Class Definition a block of code that specifies or defines the attributes and behaviors of an object Namespace A block of computer memory containing the code that defines a group or related classes (The System.Windows.Form namespace contains a definition of the Windows Form class) dot member access operator The dot between each word of the System.Windows.Forms.Form that indicates levels of namespaces where the Form object is located Name Property The Name property is what the object is referred to inside the code After changing anything in the form, an asterisk (*) appears in the name tab indicating that a change has been made since the form was opened 7

8 Text Property The Text Property controls the caption at the top of the form StartPosition Property Determines where the form is located on the screen when the program is started Options appear in the dropdown menu in the property value area Size Property A form can be resized by o Dragging edit handles o Setting the width and height properties in the Size Property Size is measured in pixels 8

9 Clicking the plus sign next to the size property expands to show the width and height sizes individually BackColor Property The BackColor property can be set by clicking the down arrow o Choose the Custom tab and pick a color Setting and Restoring the Value of a Property Right Click the BackColor Property Choose the Reset option o The property s setting will be returned to the default property o This holds true for all properties 9

10 Closing the Current Solution Click the File menu option Choose Close Solution from the menu o The Close option will only close the designer window in the IDE Opening an Existing Solution Click File and choose the Open Project option from the drop down menu Locate the desired project Click the Open Button 10

11 If the form does not open, click its form object in the Solution Explorer Then, click the View option from the menu and choose the Designer option Exiting Express Click File from the menu Choose Exit 11

12 Working with Controls Tools in the toolbox contain both an icon and a name Pointing to one of the tools results in a dialog displaying that tool s purpose Each tool represents a class with its own attributes and behaviors The Label Tool The label tool is used to display text that the user cannot edit or change during the running of the application Click and drag the Label Tool onto the form o The Label1 label appears in the form Click on the Label1 label The Name Property Click on the default name in the Name entry in the Properties Window Now the name of the label can be changed Naming Conventions For the purposes of this set of instructions, we will begin the names of all controls with the lower case letter x followed by an explanatory name for the control and finally the tool itself. For example: xauthorlabel 12

13 The Text Property Select the label on the form Highlight the default entry in the Text Property Change the property to whatever the textbox should say The Location Property Select the label Select the plus sign next to the Location Property Enter the x location (The horizontal location of the upper left corner of the label) followed by a comma, and then the y location (The vertical location of the upper left corner of the label) These settings are copied in the x and y properties Clicking the minus sign next to Location contracts the location property again The control can also be moved by clicking and dragging it on the form 13

14 Changing Several Controls Simultaneously Hold the CTRL key while clicking on as many controls as desired Each control will be included in the selection The Font Property Select the Font Property for the controls selected Click the Ellipsis button for the property o The Font Dialog Box will open From here, the font, style, and size can be set Setting Individual Font Properties Some of the properties have drop-down lists to choose from o For instance, the Name property lists all of the available font names o The desired font can be chosen by clicking on it 14

15 The Format Menu The Format Menu Option contains options to apply to selected form components Here, two labels are selected The Format Center in Form Horizontally series centers the selected controls as per the graphic to the left Options also exist to align several controls by different corners, etc. The Picturebox Tool Drag a Picturebox onto the form The picturebox control appears and includes a Task Box Clicking the Task Box lists the possible tasks available with a picturebox Here, we will Choose Image The image chooser appears and the desired image file can be chosen Click the Import Button to import the image into the picturebox Click OK 15

16 AutoSize Size Mode Click the Task Box on the picture box control Choose the Size Mode option Choose AutoSize The picture box expands to fit the entire picture o Note that the picture will not go any further than the boundary of the form The AutoSize entry appears in the picture box SizeMode entry The Normal Size Mode allows you to resize the picture box to the size desired, cropping the picture to fit the box 16

17 Button Tool Click and drag the Button Tool onto the form The Exit button below has the following properties o Name = xexitbutton o Location = 270,237 o Font = Tahoma, 12 point o Text = Exit o Size = 75,26 Starting and Ending an Application Finding the Startup Form The startup form is the default form that starts when the application is run. Right click the My Project entry in the Solution Explorer Click the Open button 17

18 The Application Form opens The Startup Form is listed in the Application Form To change the startup form, click the down arrow and choose a different form Click the Start Debugging button OR Press the F5 key on the keyboard This will create an executable file able to run outside of the IDE The executable file is located in the debug folder inside the bin folder in the Solution folder 18

19 Writing Code Event = The act of interacting with an application (i.e. Clicking a Button) Event Procedure = The code that responds to the event (i.e. Clicking the Exit button will close the application In the Solution Explorer, click the View Code button OR right click the form and choose the View Code option 19

20 Code Editor Tab Designer Tab Class Statement Collapsing Code Click the minus next to the class statement to collapse that section of code so only the class statement is visible. Class Name List Box Lists all objects included in the form Method Name List Box Lists the events to which the selected object is capable of responding Choosing the Exit Button s Click Event Choose the xexitbutton object from the Class Name List Box Then choose the Click event from the Method Name List Box 20

21 The object s Click event procedure appears in the Code Editor Window The code that appears there is the Code Template for the object that helps you follow the correct syntax for the code you want to write Procedure Header = Private Sub xexitbutton_click (ByVal sender ) Handles xexitbutton.click Procedure Footer = End Sub Keyword = A word with special meaning in the language i.e. Private Sub or End Sub o The keyword Sub is short for Sub Procedure (A block of code that performs a specific task) o xexitbutton_click = The name of the object and the event (separated by an underscore) o (ByVal sender As Object, ) = Parameters sent passed to the procedure when invoked The Me.Close Method Between the procedure header and procedure footer, the Me.Close Method can be added o Method = Predefined Visual BASIC procedure o Typing the Me.Clo text shows a dropdown list of methods that can be associated with the Me object o Continuing to type will eventually automatically select the Close method o Pressing Enter will place that code in the procedure IntelliSense = The automatic code selections as reviewed above 21

22 Sequence Structure When the Exit Button is clicked, the code inside its procedure is executed in the order (top to bottom) in which it was written. This is Visual BASIC s Sequence Structure Using the Timer Tool The timer tool is used to execute code at regular intervals. Interval Property = The length of the time interval in milliseconds (1/1000 th of a second) Enabled Property = Can be either True (Timer on) or False (Timer off) Tick Event = Occurs each time the interval elapses o Timer code is entered in the timer s Tick event procedure Drag the timer tool onto the form (The timer control will be stored in the component tray) Set the name, interval, and enabled properties as desired Removing a Control In the case of our application, since we will be using the timer to exit the application, we can delete the exit button control. Click on the control Right click and choose delete or press the delete key 22

23 Removing a Control s Code Open the Code Viewer Select the code for the deleted control (In this case, we highlight the Click event for the exit button) and press the Delete key Coding the Timer Control Code the timer s Tick event to close the application (Me.Close( )) Now, the timer will close the application after an interval of 8 seconds Setting the FormBorderStyle Property The form s border style can be any of the following: FormBorderStyle Setting Fixed3D FixedDialog FixedSingle FixedToolWindow None Sizeable SizeableToolWindow Border Description Fixed, 3-dimensional Fixed, Thick dialog style Fixed, Thin line Fixed, Tool Window style No border Sizeable normal style (Default) Sizeable, Tool window style 23

24 Select the form Click the down arrow in the FormBorderStyle property Choose the style desired MinimizeBox, MaximizeBox, and ControlBox Properties Select the form Choose the MaximizeBox or the MinimizeBox and set them to True to enable or False to disable Setting the ControlBox Property to false removes the maximize, minimize, and resize buttons from the form 24

25 Printing Code Make the code editor visible Choose the File Print options and choose the desired printer 25

26 Chapter 2 Designing Applications Programmer s Process Meet with the client Plan the application (TOE chart) a. Identify the tasks the application needs to perform i. What information, if any, will the application need to display on the screen and/or print on the printer? ii. What information, if any, will the user need to enter into the user interface to display and/or print the desired information? iii. What information, if any, will the application need to calculate to display and/or print the desired information? iv. How will the user end the application? v. Will previous information need to be cleared from the screen before new information is entered? b. Identify the objects to which you will assign the tasks c. Identify the events required to trigger an object into performing its assigned tasks d. Draw a sketch of the user interface 26

27 Build the User Interface Include different fonts Setting the font for the form sets the font for all objects contained by the form that have a font property Selecting each individual object on the form allows each individual font property to be changed for that one object Back Color Include color in the project Select the object Choose the BackColor property Click the down-arrow Choose the System Tab Choose the color Border Style Select the object Click the BorderStyle property Choose the None, Fixed Single, or Fixed 3D option 27

28 Adding a Text Box Control to the Form Click the TextBox tool and drag it to the desired location in the form (Blue snap-lines appear to help locate objects) Change its Name Property Using Another Object to Set the Size for the Textbox Select the text box to be used as a pattern for the size (The Address textbox in this case) Hold the CTRL key and click on the new textbox Click Format Make Same Size Both from the menu Locking the Controls on a Form Locking controls makes it impossible to move them until they are unlocked. Select the form (or any individual object) Right click and choose the Lock Controls options Repeating the process will unlock the objects 28

29 Assigning Access Keys An access key is a keyboard combination that selects the object without clicking the mouse. Place an ampersand ( & ) : In a button s text property In the text property of the label accompanying a text box o The tab index for the label must be one less than the tab index for its text box Generally, it is best to use the first letter as the access key Setting the TABINDEX Property Here, the ampersand was placed before the C in Calculate Order An underline appears underneath the C in the Calculate Order button s label Since the Alt C combination is reserved for the Calculate Order button, the access key for Clear Screen button should be set as the l in the word Clear The Tab Index sets the order in which objects in the form receive focus (are selected). By default, the computer sets objects tab index in the order in which they have been created. Here, the TABINDEX for the Name label is set to zero In order for the N access key to work for its textbox, that textbox access key is 1 To view the tabindex order o Choose the Tab Order option from the View button in the toolbar 29

30 In this view, the tabindex order can be changed by clicking the blue number box or the object itself o Clicking the first time reduces the index by 1 o Continuing to click increments the index each click o Clicking to the number of objects in the form restarts the numbering at zero Coding the Application Use pseudocode to summarize the function of the application or its component procedures. Pseudocode is nothing more than code written in plain English without any concern with proper syntax. Place the pseudocode in a flow chart that shows the logical order of the program 30

31 Assigning a Value to a Property During Run Time Press Enter to move the insertion point to the next line Me refers to the current form and activates intellisense Add a dot (Me.) Select the object in the form for which a property is to be edited Press Tab Add another dot Select the property (Text, in this case) Press Tab Add the operator (=) Type the value (String.) Choose Empty to clear the textbox OR Press the Ctrl Spacebar keys at the same time Type xs and the xstatetextbox is selected Press Tab and continue as above 31

32 The Focus Method During runtime, when a form object is selected and is ready to enter data or choose an option, it is said to have Focus. Here, we add a remark to the code stating that, following execution of all of the Clear button s code, focus is sent to the xnametextbox object o All remarks are preceded by an apostrophe and a space Commenting an Entire Application Above is an example of commenting a project Arithmetic Expressions Arithmetic operations follow the normal algebraic order: 1. Exponents ( ^ ) 2. Negation ( - ) 3. Multiplication and Division ( * and / ) 4. Integer Division ( \ ) Returns an Integer quotient and both numbers must be Integers 5. Modulus Arithmetic (Mod) Returns the REMAINDER and numbers DO NOT have to be Integers 6. Addition and Subtraction (+ and -) 32

33 Val Function The code above is meant to sum the total number of boards purchased and to calculate their cost but the resulting form is incorrect: Instead of adding the values 5 and 10 together, it concatenated the two numerals (5 and 10) to form 510 The resulting math created a grossly inaccurate calculation of the total cost To fix this situation, we use the Val function which changes the numeral text 5 and 10 to arithmetic values. 33

34 Format Function to Format Numeric Output The available numeric formats are: 1. Currency a. Dollar sign b. 2 decimal places c. Commas for thousands separators d. Negatives in parenthesis 2. Fixed a. At least one digit left of decimal point b. At least two digits right of the decimal point 3. Standard a. At least one digit left of decimal point b. At least two digits right of the decimal point c. Commas for thousands separators 4. Percent a. Multiplies by 100 b. Adds a percent sign ( % ) c. Two digits to the right of the decimal point Adding this code to the project: Results in this output: 34

35 Aligning the Text In a Control Select the control to align Select the down-arrow in the TextAlign property in the Properties Window Choose the desired position for the alignment o Upper Left o Upper Center o Upper Right o Center Left o Center Center o Center Right o Lower Left o Lower Center o Lower Right Here, the Total Price result is centered horizontally and vertically as the middle button was chosen for the alignment option 35

36 Testing and Debugging Prior to commissioning an application it should be tested using valid data (data that is expected) such as numbers where calculations are to be performed and invalid data such as entering names where numbers are needed to do calculations. It should also be run with blank data. All this to see if it recovers gracefully in any event. Syntax errors (errors in the typing of the code) are mostly caught as they are typed but some may exist and will need to be corrected. Logical errors are syntactically correct but the results are inaccurate. For example, misplaced or omitted parenthesis where needed will result in an answer but the calculations will be wrong. This type of error is the most insidious as, without manually checking the calculations, everything may appear accurate. Assembling the Documentation 1. Print the Interface a. Run the application b. Press ALT-Print Screen to place the screen shot on the clipboard c. Open a word processor d. Press CTRL-V to place the screen shot in the word processor e. Print the word processor document 2. Print the code a. In the application window, choose the code editor b. Choose File Print c. Select the desired printer d. Click OK e. The code will print out 36

37 Using Variables and Constants Variables and constants used in a program hold values of varying data types: Type Stores Memory Required Values Boolean Logical Value 2 bytes True / False Byte Binary Number 1 byte 0 to 255 (unsigned) Char One Unicode Character 2 bytes One Unicode Character Date Date and Time Dates from January 1, 0001 to December 31, bytes Information and times from 0:00:00 to 23:59:59 +/- 79,228,162,514,264,337,593,543,950,335 Number with no decimal point Decimal Fixed-Point +/ bytes Number Number with a decimal point +/ Smallest non-zero number Double Floating-Point +/ E-324 to 8 bytes Number E308 Integer Integer 4 bytes -2,147,483,648 to 2,147,483,648 Long Integer 8 bytes ,372,036,854,775,808 to 9,223,372,036,854,775,807 Object Object Reference 4 bytes N/A (This is the default data type) Short Integer 2 bytes -32,768 to 32,767 Single Floating-point Number 4 bytes +/ E-45 to E38 String Text Varies 0 to approximately 2 billion characters Unicode is the universal coding system used to lace a numeric value on every character in every language in the world. Naming a Variable A variable s name is also referred to as its identifier. Older naming conventions created identifiers with the first 3 characters referring to the data type. Newer versions simply use names that refer to the purpose of the variable s data. 37

38 Naming Rules Must begin with a letter or an underscore Can contain only letters, numbers, and underscore Can consist of over 16,000 characters but is recommended to limit size to no more than 32 characters Cannot be a reserved word (Such as a function name etc.) Declaring a Variable The syntax of variable declaration is: {Dim Private Static} <variable name> as <data type> {= initial value} For example: Dim counter as Integer Dim myname as String = John Q. Public Usually, variable names consisting of more than 1 word start with the first word all in lower case and follow with the first letter of all succeeding words capitalized (i.e. myname). Assigning Data to an Existing Variable Use of the equal sign ( = ) assigns a value stored in the memory location for that variable, For example: myname = John Q. Public assigns the value John Q. Public to the memory location for the variable myname. startingsalary = assigns the value to the memory location for the variable startingsalary In the above examples, John Q. Public is a string literal constant and is a numeric literal constant. 38

39 Literal Type Characters Using a type character when assigning a value to a variable forces the literal constant to assume a data type other than the variable s current type. Literal Type Character Data Type Example S Short age = 35S I Integer hours = 40I L Long population = 20500L D Decimal rate =.03D F Single payrate =.03F R Double sales = 2356R C Char initial = A C The TryParse Method All numeric classes include the TryParse Method which can be used to convert a string to that numeric data type. Syntax: <datatype>.tryparse(string, variable) Example: Dim numberofbooks as Integer Integer.TryParse(Me.xBooksSold.Text, numberofbooks) Strings that contain a dollar sign, parenthesis, percent sign, letter, or space CANNOT be converted to a numeric value and the value zero will be assigned to the numeric variable, In the example above, if the text in the xbookssold text box contained one of these characters, the value zero would be assigned to numberofbooks. Conversion can be done if the text string contains only numbers, a decimal point, a leading or trailing sign, a comma, or leading and/or trailing space. In this way, data stored as text can be checked to be sure it is numeric and can be used for calculations. 39

40 The Convert Class The Convert class converts numeric data types to another specified data. The Convert class includes the following methods: ToDecimal ToDouble ToInt32 ToString Syntax: Convert.<method>(value) Example: Dim numberofbooks as Integer Dim bookcount as String bookcount = Convert.ToString(numberOfBooks) OR Dim numberofbooks as Integer Dim bookcount as String = Convert.ToString(numberOfBooks) OR Dim bookcount as String = Convert.ToString(73) Using a Variable in an Arithmetic Expression When a variable is used in an arithmetic expression, its value stored in memory is used in the calculations. Line Continuation Character Placing an underscore in the line of code continues it in the next line: Rules: 1. Must be immediately preceded by a space 2. Must be at the end of the physical line of code 40

41 Scope and Lifetime of a Variable Scope = Where in the code the variable can be used Lifetime = How long the variable remains in the computer s memory 1. Procedure Level Variable = The variable is declared in a procedure and has procedure scope 2. Module Level Variable = The variable is declared in the form s declaration section (begins with Public Class), giving that variable module scope Module level variables are used by more than on procedure in the form Variables are declared using the Private keyword instead of Dim 3. Block Level Variable = The variable is declared within specific blocks of code and are have block scope For instance, the variable may be created inside a loop Static Variables A static variable is a procedure level variable that maintains its value even after the procedure ends. Use the Static keyword to declare the variable Use static variables instead of module level variables because the smaller the scope, the less likely the variable will be inadvertently used elsewhere causing possible problems Named Constants A named constant has a memory location but its value cannot be changed at runtime. Declared using the Const statement Example: Private Const Pi as Double = 3.14 Example: Dim Const SunDistance as Integer = 93,000,000 Named using Pascal Case (The first letter of EVERY WORD in the name is capitalized) Option Explicit and Option Strict 1. Option Explicit a. On its own, Visual BASIC will create any undeclared (Dim, Private, Static) variable during the course of the run. This often happens if a previously declared misspelled variable is assigned a value. b. Option Explicit disallows the creation of undeclared variables, thus eliminating the problem c. Syntax: Option Explicit On d. Placed in the General Level of the Project 41

42 2. Option Strict a. If a variable is declared as a given data type and is mistakenly assigned a value outside of this data type, Visual BASIC will convert the value to fit the memory location (implicit type conversion). b. This can be harmless if the variable is promoted to a data type that accepts data larger than its original (i.e. Converting 7 to 7.0 will not produce problems) c. If the variable is demoted to a less inclusive data type, calculation errors could happen (i.e is assigned to an Integer data type, rounding the value to its nearest whole number (7) Thus causing possible calculation errors) d. Option Strict disallows the misappropriation of values to variables e. Syntax: Option Strict On f. Placed in the General Level of the Project Concatenating Strings To concatenate a string is to place additional character(s) into it. The concatenation operator is the ampersand ( & ) The result of the code above is shown on the left 42

43 The InputBox Function In this example, an input box will be established in the form s Load event: Choose the MainForm Events option from the Class Name dropdown Choose the Load procedure from the procedures dropdown The syntax for an input box is InputBox(prompt, [title], [default response]) The title and default response are optional. Here, string constants have been established for the input prompt (InputPrompt) and the title (InputTitle). Note that the string literals could have just as easily been used in the command. Here is the resulting input box. Entering text in the text box and clicking OK or pressing Enter will assign that string to the salesperson variable. 43

44 Here, the code was changed to: salesperson=inputbox(inputprompt,inputtitle, Sales Department ) Here, the code was changed to: salesperson=inputbox(inputprompt,, Sales Department ) Note that the title was replaced with a set of blank commas as place holders. The title area of the input box was then changed to the title of the solution. 44

45 ControlChars. NewLine Constant The ControlChars.NewLine constant is used to split strings into separate lines. Here, the name of the sales person was added to the xmessagelabel on a new line by adding the ControlChars.NewLine constant to the string: Designating a Default Button Setting a default button means that the button will execute its associated code when the ENTER key is pressed even when it does not have focus. Set the form s AcceptButton property to the xcalculatebutton. This will make it possible to execute that button s code whenever the ENTER key is pressed. 45

46 Format Numbers with ToString The syntax of the ToString method is: <variable name>.tostring(formatstring) Format Specifier C or c D or d F or f N or n P or p Name Currency Decimal Fixed-Point Number Percent Description Number with dollar sign Precision specifier indicates number of decimal places (I.e. C2) Thousands separator if necessary Negatives in parenthesis Formats only integers Precision specifier indicates minimum number of digits (i.e. D3) Padded with zeroes to the left if necessary to reach specified digits Negatives preceded by minus Precision specifier indicates number of decimal places (i.e. F0) Negatives preceded by minus Precision specifier indicates number of decimal places (i.e. N4) Thousands separator if necessary Negatives preceded by minus Precision specifier indicates number of decimal places (i.e. P1) Multiplies the number by 100 Displays with a percent sign Negatives preceded by minus formatted as ToString( C2 ) $ formatted as ToString( D3 ) formatted as ToString( F1 ) formatted as ToString( N4 ) formatted as ToString( P0 ) 77% Here, the total price label was formatted for currency with 2 decimal places. 46

47 Using a Static Variable A static variable is created at the procedure level but maintains its value in memory (even if the procedure in which it was created ends) until the entire application ends. Here, the salesperson variable has been created as static Its value will remain in memory even after the xcalcbutton procedure has finished TextChanged Event Procedure This event occurs whenever the text property of an object is changed (Deleted or otherwise changed). Here, the code entered in the xbluetextbox s TextChanged event states that the three labels listed are to be emptied as soon as any change occurs it xbluetextbox 47

48 Associating a Procedure with Different Objects and Events In the example below, the xbluetextbox.textchanged procedure was changed to the ClearControls procedure (1). Then, the underscore (used for line continuation) was added after the parenthesis (don t forget to add a space between the parenthesis and the underscore) to continue the line below the first line (2) Then, the list of controls to be handled by the ClearControl procedure was added in the following line, separated by commas (3) Now, whenever text is changed in either box, the text properties in the three labels listed in the procedure are set to String.Empty. If Then Else Statement Many times, if/then/else statements utilize comparison operators: = Equal To <> Not Equal To > Greater Than < Less Than >= Greater Than or Equal To <= Less Than or Equal To Arithmetic operators are evaluated before comparison operators so: 3 2 > 7 * 5 is evaluated as (3 2) > (7 * 5). 48

49 Below is an example of a program that takes two integers from each of two text boxes and checks to see which one is bigger so it can assign it to the second variable with the lower number being assigned to the first variable. The results are then displayed in a label. 1 2 An IF/THEN structure is used to decide if the first integer is larger than the second (1). Note that a variable to temporarily hold the value of the first variable is created inside the IF/THEN structure (2). Since this variable is created inside this block of code, it is said to have BLOCK SCOPE. That is, it is only recognized inside that i.f/then block and cannot be used by the procedure itself. Here, a IF/THEN/ELSE block is used in an application that either adds or multiplies two numbers depending upon the number entered in the operation text box (1 for addition and 2 for multiplication) 49

50 Logical Operators Operator Operation Precedence Not Reverses the truth value 1 And Indicates that all parts of compound truth must be true for the entire truth to be true 2 AndAlso Same as AND but it performs short circuit evaluation 2 Or Indicates that only one part of a compound truth need be true for the entire truth to be true 3 OrElse Same as OR but it performs short circuit evaluation 3 Xor One and only one part of a compound truth can be true for the entire truth to be true 4 Short circuit evaluation means that, as soon as sufficient information is gathered about a truth, evaluation ends (i.e. X = 5 In the truth IF X < 10 OR X = 7 analysis of the truth ends as soon as it is known that the first part of the truth makes the entire truth true. Analysis of whether or not X = 7 is never done.) In the example above, when the xcalcbutton is clicked, the program gets the hours worked from that text box (1). Then, it asks if the hours worked are both greater than zero AND less than or equal to 40 (2). If so, it calculates the gross pay and displays it in the xgrosslabel as currency with two decimal places (3). If not, it places the word Error in that label (4). 50

51 Comparing Strings Containing Letters Upper and lower case letters DO NOT HAVE THE SAME VALUE in Visual BASIC. So, a K is not equal to a k. This is because the UNICODE value for each is different. Therefore the truth: If K = k will return FALSE. 1 Converting String Cases Above is an example of code that uses ToUpper (1) and ToLower (2) to change the case of a string. Comparing Boolean Values

52 In the code above, the IsNullOrEmpty method is used to determine if there is text in the xnametextbox (1). Then, an IF/THEN/ELSE structure is used to determine what response should be printed in the xmsglabel text box (2) Above, the Boolean variables isoldok and israteok are created (1). Then, the TryParse method (which returns a Boolean value of true or false) is used to determine if the value in the two text boxes can indeed be changed to numeric values (2). Finally, a IF/THEN/ELSE structure is used to determine what should be displayed in the xnewpaylabel text box (3). 52

53 Chapter 4 Lesson B Adding a Group Box to a Form The GroupBox tool is located in the Containers section of the toolbox (1). It can physically separate a group of controls from other controls. 1 The Text property of the control appears in the group box. To remove it, remove all text from the Text property. Choosing Format Center in Form Horizontally or Vertically will center the objects within the GroupBox, not within the form. 53

54 The Tab Order can be set using the View Tab Order The newly created group box appears as #10 on the tab order list. Click each order number to reorder. 54

55 Financial.Pmt Method This method calculates the periodic payments for loans or investments. Syntax: Financial.Pmt(Interest Rate, Number of periods, Present/Future value, Due date) Interest Rate The interest rate per pay period (i.e. 5% is.05) Number of Periods Number of payments during the course of the loan or investment (i.e. 10 years in monthly payments is 10 * 12) Present Value For a loan, it s the loan amount. For an investment, it s zero. Future Value For a loan, it s zero. For an investment, it s the target saving amount. Due Date of Payments Can be DueDate.EndOfPeriod or DueDate.BeginningOfPeriod. (If omitted, it is assumed to be DueData.EndOfPeriod.) Below, is an example of a loan calculation and its subsequential placement in a label: Note, that a negative sign was placed in front of the function because the function returns a negative number. The MessageBox Method This method displays text, one or more buttons, and an icon. It is used to communicate with the user. Syntax = MessageBox.Show(text, caption, buttons, icon, <defaultbutton> An example of a message box with code appears to the left. 55

56 MessageBox Methods Argument text caption buttons icon defaultbutton Meaning Text to display in the message box Text to appear in the title bar of the message box Buttons to display in the message box MessageBoxButtons.AbortRetryIgnore MessageBoxButtons.OK MessageBoxButtons.OKCancel MessageBoxButtons.RetryCancel MessageBoxButtons.YesNo MessageBoxButtons.YesNoCancel Icon to display in the message box MessageBoxIcon.Exclamation MessageBoxIcon.Information MessageBoxIcon.Stop Button automatically selected when the message box opens MessageBoxDefaultButton.Button1 (this is the default) MessageBoxDefaultButton.Button2 MessageBoxDefaultButton.Button3 Below is another example of the MessageBox.Show method: 56

57 KeyPress Event The KeyPress event occurs when the user presses a key while that particular object is selected (has focus). This character associated with that key is sent to the event s e parameter. The e parameter can then be referenced (by using its KeyChar property) to analyze the key that was pressed. In this way, unwanted keystrokes can be identified and dealt with (by using the e parameter s Handled property) Here is how this example works: 1. Change the name of the sub-procedure to CancelKeys 2. List the objects that CancelKeys handles 3. Used the KeyChar property to check the pressed key(s) inside an if structure 4. Set the Handled property to true because the pressed key was outside of the accepted range (In this case, the procedure allows numbers 0 to 9, a backspace, and a period). If an incorrect key is pressed, it is ignored and that character will not appear. 57

58 Access Keys, 29 ampersand, 42 Application, 1 Arithmetic Expressions, 32 Auto-hide Button, 2 AutoSize, 16 BackColor property, 9 Block Level Variable, 41 Button Tool, 17 Center in Form, 53 Changing Property, 6 Class Definition, 7 Class Name List Box, 20 class statement, 20 Close, 10 Code Template, 21 Commenting, 32 Comparing Boolean Values, 51 Comparing Strings, 51 component tray), 22 Concatenating Strings, 42 Constants, 37 ControlBox Property, 24 ControlChars. NewLine, 45 Controls, 12, 14, 28 Convert Class, 40 Converting String Cases, 51 Create directory for solution, 1 Data Sources, 4 Debugging, 18, 36 Default Button, 45 Designer, 7, 11 dot member access operator, 7 Ellipsis button, 14 Enabled Property, 22 Event, 19, 20, 22, 47 Financial.Pmt, 55 Focus Method, 32 Font Dialog Box, 14 Font Property, 14 Form Designer, 5 Format Menu, 15 Format Numeric Output, FormBorderStyle, 23 GroupBox, 53 Handled property, 57 identifier, 37 If Then Else, 48 InputBox, 43 IntelliSense, 21 Interval Property, 22 KeyChar property, 57 KeyPress Event, 57 Keyword, 21 Label Tool, 12 levels of namespaces, 7 Lifetime, 41 Line Continuation Character, 40 Literal Type Characters, 39 Location Property, 13 Locking, 28 Logical Operators, 50 MaximizeBox, 24 Me, 31 Me.Close Method, 21 MessageBox, 55

59 MessageBox Methods, 56 MinimizeBox, 24 Module Level Variable, 41 Name property, 7 Named Constants, 41 Namespace, 7 Naming Conventions, 12 Normal Size Mode, 16 Open Project, 10 Option Explicit, 41 Option Strict, 41 Picturebox, 15 Printing Code, 25 Procedure Footer, 21 Procedure Header, 21 Procedure Level Variable, 41 Programmer s Process, 26 Properties Window, 6 pseudocode, 30 Removing a Control, 22 Run Time, 31 Scope, 41 Sequence Structure, 22 Size, 8 Size Mode, 16 Size Property, 8 Solution Explorer, 2, 5, 6, 11, 17, 19 StartPosition Property, 8 Startup Form, 17, 18 Static Variable, 47 Static Variables, 41 String.Empty., 48 Sub Procedure, 21 syntax of variable declaration, 38 Tab Order, 54 TABINDEX, 29 Task Box, 15 Text Property, 8, 13 TextAlign property, 35 TextChanged Event, 47 Tick Event, 22 Timer, 22 TOE chart), 26 ToString, 46 TryParse Method, 39 Val Function, 33 Variables, 37 View Code button, 19 Window Reset Layout, 4 Windows Designer Window, 7 59