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Control Structures: If...Then...Else

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Control structures are fundamental in programming as they allow you to dictate the flow of your program based on certain conditions. In VBA, the If...Then...Else statement is a powerful tool for making decisions within your code.

Key Concepts

  1. If...Then Statement: Executes a block of code if a specified condition is true.
  2. If...Then...Else Statement: Executes one block of code if a condition is true and another block if it is false.
  3. If...Then...ElseIf...Else Statement: Allows for multiple conditions to be checked in sequence.
  4. Nested If Statements: An If statement inside another If statement to check multiple conditions.

Syntax and Examples

Basic If...Then Statement

If condition Then
    ' Code to execute if condition is true
End If

Example:

Sub CheckValue()
    Dim value As Integer
    value = 10
    
    If value > 5 Then
        MsgBox "Value is greater than 5"
    End If
End Sub

If...Then...Else Statement

If condition Then
    ' Code to execute if condition is true
Else
    ' Code to execute if condition is false
End If

Example:

Sub CheckValueWithElse()
    Dim value As Integer
    value = 3
    
    If value > 5 Then
        MsgBox "Value is greater than 5"
    Else
        MsgBox "Value is 5 or less"
    End If
End Sub

If...Then...ElseIf...Else Statement

If condition1 Then
    ' Code to execute if condition1 is true
ElseIf condition2 Then
    ' Code to execute if condition2 is true
Else
    ' Code to execute if none of the conditions are true
End If

Example:

Sub CheckMultipleConditions()
    Dim value As Integer
    value = 7
    
    If value > 10 Then
        MsgBox "Value is greater than 10"
    ElseIf value > 5 Then
        MsgBox "Value is greater than 5 but 10 or less"
    Else
        MsgBox "Value is 5 or less"
    End If
End Sub

Nested If Statements

If condition1 Then
    If condition2 Then
        ' Code to execute if both condition1 and condition2 are true
    End If
End If

Example:

Sub NestedIfExample()
    Dim value1 As Integer
    Dim value2 As Integer
    value1 = 8
    value2 = 12
    
    If value1 > 5 Then
        If value2 > 10 Then
            MsgBox "Both conditions are true"
        End If
    End If
End Sub

Practical Exercises

Exercise 1: Simple If...Then

Task: Write a VBA macro that checks if a number stored in a variable is positive. If it is, display a message box saying "The number is positive."

Solution:

Sub CheckPositiveNumber()
    Dim number As Integer
    number = 15
    
    If number > 0 Then
        MsgBox "The number is positive"
    End If
End Sub

Exercise 2: If...Then...Else

Task: Write a VBA macro that checks if a number stored in a variable is even or odd. Display a message box with the result.

Solution:

Sub CheckEvenOrOdd()
    Dim number As Integer
    number = 7
    
    If number Mod 2 = 0 Then
        MsgBox "The number is even"
    Else
        MsgBox "The number is odd"
    End If
End Sub

Exercise 3: If...Then...ElseIf...Else

Task: Write a VBA macro that checks a student's score and assigns a grade based on the following criteria:

  • Score >= 90: Grade A
  • Score >= 80: Grade B
  • Score >= 70: Grade C
  • Score < 70: Grade F

Solution:

Sub AssignGrade()
    Dim score As Integer
    score = 85
    
    If score >= 90 Then
        MsgBox "Grade A"
    ElseIf score >= 80 Then
        MsgBox "Grade B"
    ElseIf score >= 70 Then
        MsgBox "Grade C"
    Else
        MsgBox "Grade F"
    End If
End Sub

Common Mistakes and Tips

  • Missing End If: Always ensure that every If statement has a corresponding End If.
  • Incorrect Condition Syntax: Ensure conditions are correctly written. For example, use = for equality, > for greater than, and < for less than.
  • Logical Errors: Double-check the logic of your conditions to ensure they cover all possible scenarios.

Conclusion

The If...Then...Else control structure is essential for making decisions in your VBA programs. By mastering this concept, you can create more dynamic and responsive code. Practice writing different conditions and using nested If statements to handle complex decision-making processes. In the next section, we will explore loops, which allow you to execute code repeatedly based on certain conditions.

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