Lesson 7 : Controlling Program Flow

7.1 Conditional Operators

To control the VB program flow, we can use various conditional operators. Basically, they resemble mathematical operators. Conditional operators are very powerful tools, they let the VB program compare data values and then decide what action to take, whether to execute a program or terminate the program and more. These operators are shown in Table 7.1.

7.2 Logical Operators

In addition to conditional operators, there are a few logical operators which offer added power to the VB programs. There are shown in Table 7.2.

Table 7.1: Conditional Operators Operator Meaning = Equal to > More than < Less Than >= More than and equal <= Less than and equal <> Not Equal to

Table 7.2:Logical Operators Operator 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

* You can also compare strings with the above operators. However, there are certain rules to follows: Upper case letters are less than lowercase letters, "A"<"B"<"C"<"D".......<"Z" and number are less than letters.

7.3 Using If.....Then.....Else Statements with Operators To effectively control the VB program flow, we shall use If...Then...Else statement together with the conditional operators and logical operators. The general format for the if...then...else statement is If conditions Then VB expressions Else VB expressions End If * any If..Then..Else statement must end with End If. Sometime it is not necessary to use Else.

Example: Private Sub OK_Click() firstnum=Val(usernum1.Text) secondnum=Val(usernum2.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

*VBTutor lesson 7