Lesson 13: If..Then..Else in VB2019

In this lesson, we'll learn about conditional operators and logical operators along with the powerful If..Then..Else keywords that form the backbone of decision-making in Visual Basic 2019.

13.1 Conditional Operators

Conditional operators resemble mathematical operators. These operators allow a Visual Basic 2019 program to compare data values and decide what actions to take. They are also known as numerical comparison operators.

13.2 Logical Operators

When you need to make more than one comparison to arrive at a decision, logical operators become essential. They can compare both numerical data and non-numeric data such as strings.

13.3 If Control Structure

To control program flow and make decisions, we use the If control structure with conditional and logical operators. There are three types:

If condition Then
    ' Code to execute
End If

If condition Then
    ' True code
Else
    ' False code
End If

If condition1 Then
    ' Code 1
ElseIf condition2 Then
    ' Code 2
Else
    ' Default code
End If

13.3(a) If...Then Statement

This structure executes code only when the condition is true. If false, no action is performed.

Example 13.1: Number Checker

This program checks if a number is between 50 and 100. If true, it shows a winning message. Otherwise, it shows a different message.

Private Sub BtnCheck_Click(sender As Object, e As EventArgs) Handles BtnCheck.Click
    Dim myNumber As Integer
    myNumber = TxtNum.Text
    
    ' Check if number is between 50 and 100
    If myNumber >= 50 And myNumber < 100 Then
        MsgBox("Congratulations! You win a lucky prize")
    End If
    
    ' Check if number is outside the range
    If myNumber < 50 Or myNumber >= 100 Then
        MsgBox("Sorry, you did not win a lucky prize")
    End If
End Sub

13.3(b) If...Then...Else Statement

This structure provides a cleaner way to handle true/false conditions by executing one block when true and another when false.

Example 13.2: Improved Number Checker

This improved version uses If...Then...Else to provide both outcomes in a single structure.

Private Sub BtnCheck_Click(sender As Object, e As EventArgs) Handles BtnCheck.Click
    Dim myNumber As Integer
    myNumber = TxtNum.Text
    
    If myNumber >= 50 And myNumber < 100 Then
        MsgBox("Congratulations! You win a lucky prize")
    Else
        MsgBox("Sorry, you did not win a lucky prize")
    End If
End Sub

Example 13.3: Dual Condition Check

This program checks two conditions: number must be at least 100 AND age must be at least 60 to win a prize.

Private Sub BtnCheck_Click(sender As Object, e As EventArgs) Handles BtnCheck.Click
    Dim myNumber, myAge As Integer
    myNumber = TxtNum.Text
    myAge = TxtAge.Text
    
    ' Both conditions must be true to win
    If myNumber >= 100 And myAge >= 60 Then
        MsgBox("Congratulations! You win a lucky prize")
    Else
        MsgBox("Sorry, You did not win any prize")
    End If
End Sub

13.3(c) If...Then...ElseIf Statement

When you need to handle multiple conditions, the If...Then...ElseIf structure provides an efficient solution.

Example 13.4: Grade Calculator

This program calculates a letter grade based on a numerical mark using ElseIf statements.

Private Sub BtnCalculate_Click(sender As Object, e As EventArgs) Handles BtnCalculate.Click
    Dim mark As Integer
    Dim grade As String
    mark = TxtMark.Text
    
    If mark >= 80 And mark <= 100 Then
        grade = "A"
    ElseIf mark >= 60 And mark < 80 Then
        grade = "B"
    ElseIf mark >= 40 And mark < 60 Then
        grade = "C"
    ElseIf mark >= 0 And mark < 40 Then
        grade = "D"
    Else
        grade = "Out of Range"
    End If
    
    MsgBox("Your Grade is " & grade)
End Sub

Next Lesson

Ready to learn about efficient multi-condition handling? Continue to Lesson 14: Select Case.

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