If Statements

If ... Then ... End If runs code only when a condition is True:

Module Program
    Sub Main()
        Dim temperature = 31

        If temperature > 30 Then
            Console.WriteLine("Stay in the shade")
        ElseIf temperature > 15 Then
            Console.WriteLine("Enjoy the weather")
        Else
            Console.WriteLine("Take a jacket")
        End If
    End Sub
End Module

Stay in the shade

• ElseIf is one word.
• The first condition that's True wins; the rest are skipped.
• Every block If needs a matching End If.

Single-line If

Short checks can go on one line, without End If:

Module Program
    Sub Main()
        Dim stock = 3
        If stock < 5 Then Console.WriteLine("Low stock: reorder!")
        If stock = 0 Then Console.WriteLine("Sold out") Else Console.WriteLine($"{stock} left")
    End Sub
End Module

Low stock: reorder!
3 left

Use the single-line form only for very simple statements; the block form is easier to read and to extend.

Nested conditions

Module Program
    Sub Main()
        Dim age = 25
        Dim hasTicket = True

        If age >= 18 Then
            If hasTicket Then
                Console.WriteLine("Welcome in")
            Else
                Console.WriteLine("Please buy a ticket")
            End If
        Else
            Console.WriteLine("Adults only")
        End If

        ' Often clearer combined:
        If age >= 18 AndAlso hasTicket Then Console.WriteLine("Welcome in (again)")
    End Sub
End Module

Welcome in
Welcome in (again)

Common mistakes

• Forgetting Then at the end of the condition line.
• Using And instead of AndAlso when the second check depends on the first.
• Writing If x = True Then — just write If x Then.

Practice

Write a program that stores a score and prints "A" for 90 or more, "B" for 80 or more, "C" for 70 or more, and "F" otherwise. Test it with 84.

Module Program
    Sub Main()
        Dim score = 84
        Dim grade As String
        If score >= 90 Then
            grade = "A"
        ElseIf score >= 80 Then
            grade = "B"
        ElseIf score >= 70 Then
            grade = "C"
        Else
            grade = "F"
        End If
        Console.WriteLine($"Score {score}: {grade}")
    End Sub
End Module

Score 84: B