Type Storage Range of Values

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1 University of Misan College of Engineering Department of Civil Engineering Course Title: Visual Basic Second Stage Fourth Lecture Visual Basic Data There are many types of data that we come across in our daily life. For example, weneed to handle data such as names, addresses, money, date, stock quotes, statisticsetc. everyday. Similarly in Visual Basic, we are also going to deal with these kinds ofdata. However, to be more systematic, Visual Basic divides data into differenttypes. 4-1 Types of Visual Basic Data a) Numeric Data Numeric data are data that consist of numbers, which can be computed mathematically with various standard operators such as add, minus, multiply, divide and so on. In Visual Basic, the numeric data are divided into 7 types, which are summarized in Table 4-1: N o. Table 4-1: Numeric Data Types Type Storage Range of Values 1 Byte 1 byte 0 to Integer 2 bytes -32,768 to 32,767 3 Long 4 bytes -2,147,483,648 to 2,147,483,648 4 Single 4 bytes E+38 to E-45 for negative values E-45 to E+38 for positive values 5 Double 8 bytes e+308 to E-324 for negative values E-324 to e+308 for positive values 6 Currency 8 bytes -922,337,203,685, to 922,337,203,685, Decimal 12 bytes +/- 79,228,162,514,264,337,593,543,950,335 if no decimal is used+/ (28 decimal places). Page1 24

2 b) Non-numeric Data Types The non-numeric data types are summarized in Table 4-2: Table 4-2: Nonnumeric Data Types No. Data Type Storage Range 1 String (fixed length) Length of string 1 to 65,400 characters 2 String (variable length) Length + 10 bytes 0 to 2 billion characters 3 Date 8 bytes January 1, 100 to December 31, Boolean 2 bytes True or False 5 Object 4 bytes Any embedded object 6 Variant (numeric) 16 bytes Any value as large as double 7 Variant (text) Length+22 bytes Same as variable-length string c) Suffixes for Literals Literals are values that you assign to a data. In some cases, we need to add a suffixbehind a literal so that VISUAL BASIC can handle the calculation more accurately.for example, we can use num=1.3089# for a Double data type. Some of the suffixes are displayed in Table 4-3: Table 4-3: Suffix No. Suffix Data Type 1 % Integer 2 & Long 3! Single 4 # Double Currency 6 $ String In addition, we need to enclose string literals within two quotations and date and time literals within two # signs. Strings can contain any type of characters, including numbers. The following are a few examples: membername$="ahmed, Dhuha" TelNumber$=" " LastDay=#31-Dec-00# ExpTime=#12:00 am# Mark%=90 profit@= It should be noted that in most cases, it is not necessary to use suffixes as long aswe declare the variables using the Dim statement. Page2 24

3 4-2 Managing Variables Variables are like mail boxes in the post office. The contents of the variables change every now and then, just like mail boxes. In terms of Visual Basic, variables are areas allocated by the computer memory to hold data. Like the mail boxes, each variable must be given a name. To name a variable in Visual Basic, you have to follow a set of rules. a) Variable Names The following are the rules when naming the variables in Visual Basic: 1- It must be less than or equal to 255 characters. 2- No spacing is allowed. 3- It must not begin with a number. 4- Periods are not permitted. Examples of valid and invalid variable names are displayed in Table 4-4: Table 4-4: valid and invalid variable names Valid Name Invalid Name My_Car My.Car This year 1NewBoy Long_Name_Can_beUSE He&HisFather *& is not acceptable Page3 24

4 b) Declaring Variables In Visual Basic, one needs to declare the variables before using them by assigning names and data types. You can declare the variables implicitly or explicitly. For example, sum=text1.text means that the variable sum is declared implicitly and ready to receive the input in the Text1 textbox. Other examples of implicit declaration are volume=8 and label="welcome". On the other hand, for explicit declaration, variables are normally declared in the general section of the code s window using the Dim statement. The format is as follows: Dim Variable Name as Data Type Dim (Private) password As StringDim: Dimension Dim yourname As String Dim firstnum As Integer Dim secondnum As Integer Dim total As Integer Dim dodate As Date Page4 24

5 You may also combine them in one line, separating each variable with a comma, asfollows: Dim password As String, yourname As String, firstnum As Integer. If the data type is not specified, Visual Basic will automatically declare the variableas a Variant. For string declaration, there are two possible formats, one for the variable-length string and another for the fixed-length string. For the variable-length string, just use the same format as Example above. However, for the fixed-length string, youhave to use the format as shown below: Dim VariableName as String * n, where n defines the number of characters the string can hold. For example, Dim yourname as String * 10 mean yourname can hold nomore than 10 Characters. Declaration of Variables There are three methods to declaration of variables: 1- Dynamic Local Variables. Syntax 2- Static Local Variables. Syntax Dim Variable Name as Variable Type Static Variable Name as Variable Type 3- Global (Public) Variables. Syntax Public Variable Name as Variable Type Using "Option Explicit" statement in the general declaration section of a program forces Visual Basic to generate an error message if a variable is not declared. This way you make sure that you are using only explicit form of variable declaration. Local (Private) and Global (Public) Variables If a variable is declared in a specific event procedure, i.e. Command1_Click (), then it is a local variable and can only be used in that event procedure with the declared format. If you want to use this variable in another event procedure, then you must declare it again. In order to make a variable available to all the controls and procedures in your program, you need to declare it as a global variable. Page5 24

6 This is done by declaring the variable in the General (declaration) event procedure. This event procedure is available through the Code Window as the first item in the "Object" drop-down list and first item in the "Procedure" drop-down list as seen in the following figure. General Declaration 1 st Variable 2 nd Variable Third Variable Page6 24

7 4-3 Constants If a variable in your program contains a value that never changes (such as π, a fixed mathematical entity), you might consider storing the value as a constant instead of as a variable. A constant is meaningful name that takes the place of a number or a text string that doesn t change. Constant are useful because the increase the readability of program code, they can reduce programming mistake, and they make global changes easier to accomplish later. Constant operate a lot like variables, but you can t modify their values at run time. In Visual Basic you can declare a constant by using the keyword "Const", as show in the following example: Const pi As Double= Constant are useful in the program code, especially in involved mathematicalformulas, such as area of circle = π r 2. Syntax In Editor CodeConst Constant Name = Value InModule Public Const Constant Name = Value Immediate Window There is a window down the Form called immediate window, which using direct to compute the mathematical operators in Visual Basic. Syntax Debug. Print or print then mathematical operators then press Enter Page7 24

8 Remember One of the outstanding features of Visual Basic is that you can accomplish a lot by writing only a few lines of code. In Visual Basic, code is also referred to as program Statement. A program statement can be as simple as a single word; Note: Beep This statement causes the computer speaker to make a beep sound. A program statement can also be quite sophisticated. One of the most usual forms of the program statements is as follows: Object Name. Property Name = Setting Exercises 1. List out all numeric and non-numeric data types. 2. State the rules in naming the variables. 3. Write five examples of valid variable names. 4. Use the Dim statements to declare three numeric variables and three nonnumeric variables. Fifth Lecture 5-1 Arithmetic Operators in Visual Basic In order to compute input from users and to generate results, we need to use various mathematical operators. In Visual Basic, except for + and -, the symbols for the operators are different from normal mathematical operators, as shown in Table 5-1. Table 5-1: Arithmetic Operators Page8 24

9 No. Operator Order of Precedence Mathematical function Example 1 ^ First Exponential 2^4=16 2 * Second Multiplication 4*3=12 3 / Third Division 12/4=3 4 \ Fourth Integer Division (discards the decimal places) 5 Mod Fifth Modulus (returns the remainder from aninteger division) 19\4=4 15 MOD 4=3 6 + Or & and - Sixth String concatenation "Visual"&"Basic"="Visual Basic" EX.8 Private Sub Form_Load() Form1.Height = 6000 Form1.Width = 5000 Form1.Caption = "Operators" Form1.BackColor =vbyellow Form1.FontName = "Times New Roman" Form1.Font.Italic = True Form1.Font.Size = 20 Command1.Caption = "Operators" Command1.Top = 4000 Command1.Left = 2000 Command1.Height = 1000 Command1.Width = 2000 Command1.FontName = "Times New Roman" Command1.FontItalic = True Command1.FontSize = 20 Page9 24

10 Private Sub Command1_Click() Print 7 \ 3 Print 7 Mod 3 Print "My" & "Name" Print 10 / 3 * 15 / 3 * 3 / 2-9 / 3 / 2 * 4 * 3 Print 4000# - 300# / 5 / 30# Print 4E-8 / 2 * 5E+8 / 6E+16 * 4E+14 * 3 Print 4 / 3 ^ 3 / 4 ^ 2 * 3 ^ 4 * 2 ^ 4 Print 27 ^ 1 / 3-200# ^ 3 * / 4 ^ 3 Print (3-3 ^ 3) / ((3 ^ ^ 3) / 3 ^ 5) / 3 ^ 4 EX.9:Example to explain utilizing the Operators. Now let s try writing a Visual Basic program to examine each of the operations mentioned above. 1- Open a new Visual Basic Project by clicking on the "New Project" on the "File"menu, and selecting Standard.EXE from the list of icons. 2- Select "Save As..." from the File menu. A dialog box appears with Form1.frm in the File Name window. Type "Operators" in place of Form1 and click "O.K." (Make sure you are in the directory that you want). Another dialog box appears with Project1.vbp in the File Name window. Type "Operators" in place of Project1 and click "O.K." 3- Develop the interface using the following information. 4- Attach code to the Interface Declarations of variables. Click on the "View Code" in the Project Window. In the "Object" drop-down list select "General" and in the "Procedure" drop-down list select" (declarations)". Type the following codes in this window. Dim x As Single Dim y As Single Dim z As Single Or you may type: Dim x, y, z As Single 5- Generate the executable file for this Program by clicking on "File" in the menu bar and choosing "Make EXE File... ". The Make EXE File dialog box appears and you will be asked if you would like to save the executable file in "Operators.exe". Accept by clicking "O.K". Page10 24

11 ToolBox and Properties Object Property Value Form TextBox TextBox TextBox Name Caption Name MultiLine Alignment Name MultiLine Alignment Name MultiLine Alignment Forecolor frmoperators The Operator Program txtnumber1 True Center txtnumber2 True Center txtresult True Center Red Label Caption First Number Label Caption Second Number Label Caption Result CommandButton1 Caption &Add CommandButton2 Caption &Subtract CommandButton3 Caption &Divide CommandButton4 Caption &Multiply CommandButton5 Caption &Integer Divide CommandButton6 Caption &Exponential CommandButton7 Caption & CommandButton8 Caption &Mod CommandButton9 Caption Reset CommandButton10 Caption &Exit Page11 24

12 Visual Programming Your program s interface or main window should look like this: Code Programming 1- Addition Double click on the Add Command Button. Visual Basic responds by opening the Code Window Type the following lines in the Code Window x = Val (txtnumber1.text) y = Val (txtnumber2.text) z = x + y txtresult.text = z 2- Subtract Double click on the Subtract Command Button. Visual Basic responds by opening the Code Window Type the following lines in the Code Window x = Val (txtnumber1.text) y = Val (txtnumber2.text) z = x - y txtresult.text = z 3- Divide Double click on the Divide Command Button. Visual Basic responds by opening the Code Window Type the following lines in the Code Window x = Val (txtnumber1.text) y = Val (txtnumber2.text) z = x - y txtresult.text = z Page12 24

13 4- Multiply Double click on the Multiply Command Button. Visual Basic responds by opening the Code Window Type the following lines in the Code Window x = Val (txtnumber1.text) y = Val (txtnumber2.text) z = x * y txtresult.text = z 5- Integer Divide Double click on the Integer Divide Command Button. Visual Basic responds by opening the Code Window Type the following lines in the Code Window x = Val (txtnumber1.text) y = Val (txtnumber2.text) z = x \ y txtresult.text = z 6- Exponential Double click on the ExponentialCommand Button. Visual Basic responds by opening the Code Window Type the following lines in the Code Window x = Val (txtnumber1.text) y = Val (txtnumber2.text) z = x ^ y txtresult.text = z 7- & Double click on &Command Button. Visual Basic responds by opening the Code Window Type the following lines in the Code Window x = Val (txtnumber1.text) y = Val (txtnumber2.text) z = x & y txtresult.text = z Page13 24

14 8- Mod Double click on the Mod Command Button. Visual Basic responds by opening the Code Window Type the following lines in the Code Window x = Val (txtnumber1.text) y = Val (txtnumber2.text) z = x Mod y txtresult.text = z Private Sub Command9_Click() txtnumber1.text = "" txtnumber2.text = "" txtresult = "" Private Sub Command10_Click() End Code Interpretation for EX.9 In the first line you are assigning the user input or the value of the Text property of the txtnumber1 Text Box to the variable x. While the program is running, user will type the first number for the operation in this Text Box. Your code will instruct Visual Basic to retrieve this value and assign it to the Text property of the txtnumber1 object. The same is true for txtnumber2 object in the second line of the code. Then the two variables xand y are added together and the result is assigned to the variable z. The variable z is then assigned to the Text property of the txtresult object that will consequently be displayedin the interface. 5-2 Operator Precedence A mathematical formula processes a combination of variables and operators. Following is a valid Visual Basic program statement: X = / 4-1 * 3^2 Above calculation may have several different results depending on which operator is executed first. For example is 12 added to 8 and the result is then divided by 4 or -9 is first divided by 4 and the result is added to 20? Visual Basic executes mathematical operators in a specific order. Table 5-1: Shown the order of precedencethat operators are executed in Visual Basic. Page14 24

15 In the above expression 3^2 is executed first. Then 9 (the result of 3^2) is multiplied by -1 and 8 is divided by 4. The above expression reduces to: Which will add up to 5. X = / 4-1 * 3^2 When writing formulas in Visual Basic, it is recommended to use parentheses to separate calculations. In Visual Basic, parentheses take precedence over everything else. Innermost parentheses are always executed first regardless of the operators they contain. Therefore use of parentheses forces precedence in calculations. Consider the following expression: y = 3 + 5^2 / 9 * 2^3 10 If we present this expression in this format to Visual Basic the result will be , but this expression should resemble the following formula: yy = Above expression has a value of To make sure that the formula is presented to the Visual Basic correctly, we must use parentheses. So the expression should be written as: Y = (3 + 5^2) / (9 * 2^3-10) Which will result in the correct answer. EX.10: Convert the following sentence from the algebraic formula to Visual Basic formula. 33 ee55 + ssssss 3333 llllll(22) + tttttt 3333 Solution: ((EXP(5)+SIN(30* /180))/(LOG(2)/LOG(10)+TAN(35* /180)))^(1/3) Page15 24

16 H.W:Convert the following sentences from the algebraic formula to Visual Basic Language. 1- ππ 4 UU aaaa UU bb± bb2 4aaaa aaaa 2aa Page16 24

17 6-1Conditional Operators Sixth Lecture To control the Visual Basic program flow, we can use various conditional operators. Basically, they resemble mathematical operators. Conditional operators are very powerful tools which let the Visual Basic program compare data values and then decide what action to take, whether to execute or terminate the program etc. These operators are shown in Table (5-2). Table 5-2: Comparison Operators (Conditional Operators) Operator Meaning = Equal to > More (Greater) than < Less than >= More (Greater)than or equal to <= Less than or equal to <> Not equal to The following table shows some conditional expressions and their results.you ll work with conditional expressions several time in this Course. Conditional Expression Result 10 <> 20 True (10 is not equal 20) Score <20 True if Score is less than 20; otherwise, false Score = Label 1.Text True if the Text property of the Label 1 object contains the same value as the Score variable; otherwise, false TextBox1 ="Bill" True if the word "Bill" in the TextBox1 object; otherwise, false 6-2 Logical Operators In addition to conditional operators, there are a few logical operators that offer added power to the Visual Basic programs. They are shown in Table (5-3). Table (5-3) Operators Meaning And Both sides must be true Or One side or other must be true Xor One side or other must be true but not both Not Negates truth The following table lists some examples of the logical operators at work. In the expressions, it is assumed that the Vehicle string variable contains the value "Bill", and the integer variable Price contains the value 200. Logical expression Vehicle="Bill" And Price <300 Vehicle="Car" Or Price <500 Vehicle="Bill" Xor Price <300 Not Price <100 Result True (both conditions are True) True (one condition is True) False (both conditions are True) True (condition is False) Page17 24

18 6-3Conditions Statement Conditional structures allow applications written in Visual Basic to respond to different situations depending upon the result of a test condition. The condition can be a comparison or any expression that evaluates to a numeric value If Then Statement In general, you use an If...Thenstatement when your program must make an "either/or" decision. When your program must select from more than one alternative, use an If...Then...Elsestatement, an If...Then...Elseifstatement, or a Select Casestatement. You choose the structure that is most efficient for your needs. These other statements are covered in subsequent topics If...Thenstatements evaluate whether a condition is true or false and direct the program s flow accordingly. If...Thenstatements can use either single-line or block form syntax. Syntax 1 If Condition Then Statements EX.11: What will appear when the following program is executing? Private Sub Command1_Click() X = 5 Y = 7 If X <> Y Then X = 2 * X Print "X="; X, "Y="; Y If...Then...Else statements are an elaboration on the If...Thenconcept. AnIf...Then...Else block allows you to define two blocks of code and have your programexecute one based upon the result of a condition. If more than one of the conditionsin a conditional structure is true, only the code statements enclosed by the first truecondition are executed. Syntax 2 If Condition Then Statements1 Else Statements2 Note:Can using the function IIF instead of IF Then. IIF (Condition, Statements1, Statements2) Switch (Condition1, Statements1,Condition2, Statements2) Page18 24

19 An If...Then...Else statement includes a condition that evaluates to True orfalse, one or more statements that execute depending on the result of the testcondition, and an End If statement in the case of a block If...Then...Else statement. EX.12: What will appear when the following program is executing? Private Sub Command1_Click() x = 5: y = 10: z = 30 If x <> 2 Then y = y + x z = z + x x = 0 Else y = y - x z = z - x x = 1 Print "X="; x Print "Y="; y Print "Z="; z End If Syntax 3 Syntax 4 IfConditionThenStatements End If If Condition ThenStatements ElseIf Condition n ThenStatements ElseStatements End If EX.13: Using Operators with IIf. Private Sub Command1_Click() Dim X As Integer X = Val(Text1.Text) Label1 = IIf(X >= 50, "Good", "Bad") Label1 = Switch(X >= 50, "Good", X<50, "Bad") EX.14: Using Operators with If Then Else. Private Sub Command1_Click() sage = Val(Text1.Text) If sage > 24 And sage <= 45 Then Label1 = "Acceptable" Else Label1 = "Unacceptable" End If Page19 24

20 EX.15: Using Operators with If Then Else. Private Sub Command1_Click() FirstNum = Val(Text1.Text) SecondNum = Val(Text2.Text) Total = Firstnum + SecondNum If Total = Val(Text3.Text) And Val(Text3.Text) <> 0 Then Label1.Caption = "Yes, you are Correct" Else Label1.Caption = "Sorry, you are wrong" End If EX.16 Using If Then Else. Private Sub Command1_Click() x = 8: y = 8 If x > 10 Then x = x + 7 Else If x < 5 Then x = x + 13 Else If y < 10 Then y = y + x Else y = y * 2 End If End If End If Print x, y EX.17: Using If Then ElseIf Else. Private Sub Command1_Click() x = 3: y = 10 If x > 5 Then x = x + 7 ElseIf x < 5 Then x = x + 13 ElseIf y < 10 Then y = y + x Else y = y * 2 End If Print x, y Page20 24

21 6-3-2 Select Case Statement Allow your program to choose from more than two alternatives. However, the Select Case structure can be more efficient because it evaluates the test expression onlyonce. The result of the expression is then compared against multiple values todetermine which code block is invoked.the following example shows the code syntax for the Select Case structure.one of several groups of statements is run, depending on the value of an expression. Syntax Select Case variable Case value 1 Statements executed if value 1 matches variable Case value 2 Statements executed if value 2 matches variable Case value n Statements executed if value n matches variable Case Else Statements executed if value no matches is found End Select Ex.18: Using Operatorswith Select Case. Private Sub Command1_Click() Dim age As Integer age = Val(Text1.Text) Select Case age Case is >=16 Label1 <= "you can drive now" Case 18 Label1 = "you can vote now" Case 21 Label1 = "you can travel" Case 65 Label1 = "time to retire and have fun" Case Else Label1 = "you re a great age!, Enjoy it" End Select Page21 24

22 EX.19:Using ListBox and Select Case. Private Sub Form_Load() List1.AddItem "Green" List1.AddItem "Yallow" List1.AddItem "Blue" List1.AddItem "Red" List1.AddItem "White" List1.AddItem "Black" Private Sub List1_Click() Dim icolor As Integer Dim sbackground As String icolor = List1.ListIndex Select Case icolor Case 0 sbackground = vbgreen Case 1 sbackground = vbyellow Case 2 sbackground = vbblue Case 3 sbackground = vbred Case 4 sbackground = vbwhite Case 5 sbackground = vbblack End Select Form1.BackColor = sbackground EX.20: Private Sub Command1_Click()Label3 = "Very Good" Dim degree As Single Case 90 To 100 If IsNumeric(Text1.Text) ThenCase 90 To 100 degree = Val(Text1.Text) Label3 = "Excellent" Select Case degreecase Is > 100 Case 0 To 49MsgBox "Higher degree must be <=100" Label3 = "Fail"Case Else Case 50 To 59End Select Label3 = "Pass"Else Case 60 To 69MsgBox "Your degree is wrong" Label3 = "Pass-High"End If Case 70 To 79 Label3 = "Good" Case 80 To 89 Page22 24

23 6-3-3 GoTo Statement Another branching statement, and perhaps the most hated statement inprogramming, is the GoTo statement. However, we will need this to do Run-Timeerror trapping. The format is GoTo Label, where Label is a labeled line.labeled lines are formed by typing the Label followed by a colon. Syntax GoTo Example: Line10:. Sub A: Statement GoTo Beta Statement GoTo A Statement Beta: GoTo Line10. When the code reaches the GoTo statement, program control transfers to the linelabeled Line10. Ex.21: Using GoTo Statement and Numeric Data Type as Integer Private Sub Command1_Click() Dim x, y, Max As Integer x = Val(Text1.Text) y = Val(Text2.Text) Max = x If x > y Then GoTo 10 Max = y 10 Text3.Text = Max Page23 24

24 6-3-4With End With Statement Syntax EX.22: Using With Statement Label1.Caption = Your Label1.BackColor = vbgreen Label1.ForeColor = vbblue With Label1.Caption = Bibo.BackColor = vbgreen.forecolor = vbblue End With With Object. Property = Setting End With Choose Statement Syntax Value = Choose (Number, Value1, Value2, Value n) EX.23: Using With and Choose Statement Private Sub Command1_Click() With Label1.ForeColor = vbred.backcolor = vbwhite End With T = Text1.Text Label1 = Choose(T, 20, 40, 60, 80) H.W: Write a program using the Select Case statement to inform a person about his/her eight status based on the body mass index (BMI) where BMI=bodyweight in kilograms dividedby the square of the height in meters. The weight status is usually shown in the table below: BMI BMI Weight Status Below 18.5 Underweight Normal Overweight 30.0 And Above Obese Page24 24