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Lesson 6 : Working with Variables


6.1 Assigning Values to Variables

After declaring various variables using the Dim statements, we can assign values to those variables. The syntax of an assignment is

Variable=Expression

The variable can be a declared variable or a control property value. The expression could be a mathematical expression, a number, a string, a Boolean value (true or false) and more.

The following are some examples variable assignment:

firstNumber=100
secondNumber=firstNumber-99 
userName="John Lyan"
userpass.Text = password 
Label1.Visible = True 
Command1.Visible = false 
Label4.Caption = textbox1.Text 
ThirdNumber = Val(usernum1.Text) 
X = (3.14159 / 180) * A
 

 

6.2 Operators in Visual Basic

To compute inputs 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 6.1.

Table 6.1: Arithmetic Operators
Operator Mathematical function Example>

^

Exponential

2^4=16

*

Multiplication

4*3=12,  

/

Division

12/4=3

Mod

Modulus (returns the remainder from an integer division)

15 Mod 4=3   

\

Integer Division(discards the decimal places)

19\4=4

+ or &

String concatenation

"Visual"&"Basic"="Visual Basic"

Example 6.1

Private Sub Command1_Click()

Dim firstName As String
Dim secondName As String
Dim yourName As String

firstName = Text1.Text
secondName = Text2.Text
yourName = secondName +"" + firstName
Label1.Caption = yourName
End Sub

In Example 6.1, three variables are declared as string. For variables firstName and secondName will receive their data from the user’s input into textbox1 and textbox2, and the variable yourName will be assigned the data by combining the first two variables.  Finally, yourName is displayed on Label1.

Example 6.2

Dim number1, number2,number3 as Integer
Dim total, average as variant
Private sub Form_Click()

number1=val(Text1.Text) 
number2=val(Text2.Text) 
number3= val(Text3.Text)
Total=number1+number2+number3
Average=Total/5 
Label1.Caption=Total
Label2.Caption=Average
End Sub

In the Example 6.2, three variables are declared as integer and two variables are declared as variant. Variant means the variable can hold any data type. The program computes the total and average of the three numbers that are entered into three text boxes.

Example 6.3 Easy Math

This is a simple math drill program where the user enter two numbers and calculate its sum. The program will tell him whether the answer is right or wrong. To add some gist to the program, the user needs to enter the password before he or she can proceed.

The Code
Dim password As String
Dim yourName As String
Dim firstnum As Integer
Dim secondnum As Integer
Dim total As Integer
Dim doDate As Date

Private Sub Command1_Click()
If userpass.Text = password Then
Label2.Visible = True
number1.Visible = True
number2.Visible = True
sum.Visible = True
Label3.Visible = True
Command3.Visible = True
usernum1.Visible = True
usernum2.Visible = True
OK.Visible = True
Label4.Visible = True
Label4.Caption = textbox1.Text
textbox1.Visible = False
userpass.Visible = False
username.Visible = False
Label1.Visible = False
Command1.Visible = False
Else
userpass.Text = ""
userpass.SetFocus
End If

End Sub

3.'
Private Sub Form_Load()
password = "liewxun"
End Sub

Private Sub OK_Click()
firstnum = usernum1.Text
secondnum = usernum2.Text
total = sum.Text
If total = firstnum + secondnum And Val(sum.Text) <> 0 Then
correct.Visible = True
wrong.Visible = False
Else
correct.Visible = False
wrong.Visible = True
End If

End Sub
The Output
Figure 6.1 The Login dialog
Figure 6.2




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