Conditions (if, select case, logical operations) in Visual Basic

Conditions are vital parts of any application as this is usually what drives the logic of an application.

There are multiple options available in Visual Basic to execute certain code based on the condition

If Statement

This is the most common way to decide if the code within the If statement body should be executed. If statement simply evaluates the expression to Boolean True or False and executes the code if expression is True. This means that all expressions must result in either True or False value

If True Then
    Debug.Print "Always Prints"
End If

However the following code will result in the runtime exception as String value cannot be cast to Boolean

If "A" Then
End If

while the following snippet is valid as comparison of 2 String values results into the Boolean value

If "A" = "A" Then
End If

Fallback Value

It is possible to specify the fallback value for the statement, i.e. block of code which should be executed if the main condition is False

Sub main()

    Dim myVar As Integer
    myVar = 25
    
    If myVar > 10 Then
        Debug.Print "Value of myVar variable is greater than 10"
    Else
        Debug.Print "Value of myVar variable is lower than 10"
    End If

Multiple Сonditions

It is possible to specify multiple conditions as well as combine the expressions with logical operations

Sub main()

    Dim myVar As Integer
    myVar = 25
    
    If myVar < 0 Then
        Debug.Print "myVar has a negative value"
    ElseIf myVar = 0 Then
        Debug.Print "myVar equals to 0"
    ElseIf myVar > 0 And myVar < 10 Then
        Debug.Print "myVar value in a range of 0...10 (exclusive)"
    Else
        Debug.Print "Value of myVar is 10 or more"
    End If
    
End Sub

Conditions are executed one-by-one until the True condition is found

Select Case

If it is required to perform the check against multiple constant values, instead of using If-ElseIf it is possible to use Select Case. Although, Select Case can be considered redundant to If-ElseIf, it is widely used as it allows to create a simple, more readable code. Select Case statement also supports fallback value using the Case Else statement.

The below code converts the position of the day in the week to its text representation. It throws an error if the specified value is outside of 1-7 range as this would be an invalid input.

Sub main2()

    Dim dayOfTheWeek As Integer
    dayOfTheWeek = 3
    
    Select Case dayOfTheWeek
        Case 1
            Debug.Print "Monday"
        Case 2
            Debug.Print "Tuesday"
        Case 3
            Debug.Print "Wednesday"
        Case 4
            Debug.Print "Thursday"
        Case 5
            Debug.Print "Friday"
        Case 6
            Debug.Print "Saturday"
        Case 7
            Debug.Print "Sunday"
        Case Else
            Err.Raise vbError, "", "Value outside of the 1...7 range"
    End Select

End Sub

Logical Operators

Visual basic supports 3 logical operators: And, Or and Not

• Result of And operators will be equal to True if all of its arguments are equal to True
• Result of Or operators will be equal to True if at least one of its arguments is equal to True
• Not operator reverses the value

Operators can be grouped with parenthesis to define the order of operations

Sub main3()
    
    Dim varA, varB, varC, varD As Boolean
        
    varA = True
    varB = False
    varC = True
    varD = False
    
    Debug.Print varA And varB 'False
    Debug.Print Not (varA And varB) 'True
    Debug.Print varA And varC 'True
    Debug.Print varA Or varC 'True
    Debug.Print varA Or varB 'True
    Debug.Print varB Or varD 'False
    Debug.Print (varA Or varB) And varD 'False
    Debug.Print varA Or (varB And varD) 'True
    
End Sub

The following table demonstrates the results based on the values and operator

Value1	Value2	Operator	Result
True	True	And	True
True	False	And	False
False	True	And	False
False	False	And	False
True	True	Or	True
True	False	Or	True
False	True	Or	True
False	False	Or	False
True	N/A	Not	False
False	N/A	Not	True