In previous lessons, we have learned how to create Visual Basic code that can accept input from the user and display the output without controlling the program flow. In this chapter, you will learn how to crreate VB code that can make decision when it process input from the user, and control the program flow in the process. Decision making process is an important part of programming because it can help to solve practical problems intelligently so that it can provide useful output or feedback to the user. For example, we can write a program that can ask the computer to perform certain task until a certain condition is met.
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.
In addition to conditional operators, there are a few logical operators that offer added power to the VB programs. They are shown in Table 7.2.
Table 7.1: Conditional Operators
Table 7.2:Logical Operators
* 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.
To effectively control the VB program flow, we shall
use If...Then...Else statement together with the conditional operators and
The general format for the if...then...else statement is
If conditions Then
* any If..Then..Else statement must end with End If. Sometime it is not necessary to use Else.
Private Sub OK_Click()
If total=firstnum+secondnum And Val(sum.Text)<>0 Then
correct.Visible = True
wrong.Visible = False
correct.Visible = False
wrong.Visible = True
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