2.3.1 Control Structures: If...Then...Else Statements

Control structures like If...Then...Else are used to control the flow of execution in a program based on certain conditions. The If...Then...Else statement in VBA allows the program to execute specific blocks of code based on whether a condition is true or false. It is one of the most fundamental control structures, enabling decision-making in your program.

1. Syntax of If...Then...Else

The basic syntax of the If...Then...Else statement is:

If condition Then
    ' Code to execute if condition is True
Else
    ' Code to execute if condition is False
End If

• condition: An expression that returns a Boolean value (True or False).
• Then: Indicates the start of the code block that will execute if the condition is True.
• Else: The optional part where you specify what should happen if the condition is False.
• End If: Marks the end of the If statement block.

Example:

Dim score As Integer
score = 75

If score >= 50 Then
    MsgBox "You passed the exam!"
Else
    MsgBox "You failed the exam."
End If

In this example, the condition checks if score is greater than or equal to 50. If the condition is True, it will show a message box saying "You passed the exam!", otherwise, it will show "You failed the exam."

2. Nested If...Then...Else Statements

You can nest multiple If...Then...Else statements inside each other to evaluate more complex conditions. This is useful when you need to check multiple conditions in a hierarchical manner.

Example of Nested If...Then...Else:

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

In this example, the program checks for the highest possible grade first (90 or above), then checks for the next level (80 or above), and so on. Only one block of code is executed based on the first true condition.

3. Using ElseIf

The ElseIf keyword allows you to test multiple conditions without using nested If...Then...Else blocks. It is used when you have more than two possible conditions to check.

Example:

Dim age As Integer
age = 25

If age < 18 Then
    MsgBox "You are a minor."
ElseIf age >= 18 And age < 60 Then
    MsgBox "You are an adult."
Else
    MsgBox "You are a senior."
End If

Here, the code checks the age and determines whether the person is a minor, an adult, or a senior.

4. Using Logical Operators in If...Then...Else

You can use logical operators like And, Or, and Not to combine multiple conditions within a single If statement. This allows for more complex evaluations.

Example using Logical Operators:

Dim age As Integer
Dim hasPermission As Boolean

age = 20
hasPermission = True

If age >= 18 And hasPermission = True Then
    MsgBox "You are allowed entry."
Else
    MsgBox "You are not allowed entry."
End If

In this example, both conditions (age and permission) need to be true for the program to execute the first block of code. If either condition is false, the second block will execute.

5. Using Select Case Instead of If...Then...Else

In some situations, using Select Case might be more efficient or clearer than multiple If...Then...Else statements, especially when you need to check many possible values for a single variable.

Example of Select Case:

Dim grade As String
grade = "B"

Select Case grade
    Case "A"
        MsgBox "Excellent!"
    Case "B"
        MsgBox "Good job!"
    Case "C"
        MsgBox "You passed."
    Case Else
        MsgBox "Invalid grade."
End Select

The Select Case structure is typically used when you have several specific values to check for, making the code more readable and easier to manage.

6. Shortened If Statements (Inline If)

In VBA, you can write a shortened version of the If...Then statement known as an inline If or a ternary expression, using the IIf function. This function allows you to return one of two values based on a condition.

Syntax of IIf Function:

result = IIf(condition, value_if_true, value_if_false)

Example:

Dim age As Integer
Dim result As String

age = 25
result = IIf(age >= 18, "Adult", "Minor")
MsgBox result

In this example, if the condition age >= 18 is true, it returns "Adult"; otherwise, it returns "Minor". The result is then displayed in a message box.

7. Conclusion

The If...Then...Else statement is a powerful tool in VBA, allowing you to introduce decision-making capabilities into your program. Whether using simple conditional checks, nested conditions, logical operators, or the IIf function, this control structure gives you the flexibility to execute different blocks of code depending on the outcomes of specific conditions. Properly leveraging If...Then...Else statements will help you write dynamic and responsive programs in VBA.