Do Until

All loops in VB.NET have a similar purpose. They cause a block of statements to repeat a certain number of times. The Do Until loop is similar to the Do While loop.

Notes, syntax

Do Until uses a slightly different syntax than Do While. In this loop, the Until condition causes termination when it evaluates to True.

This program uses both a Do Until loop and a Do While loop. The Do Until loop has the condition "i = 10". This loop will continue repeating until the variable "i" is equal to ten.

Module Module1
    Sub Main()
        Dim i As Integer = 0

        ' Example Do Until loop.
        Do Until i = 10
            Console.WriteLine("Do Until: {0}", i)
            i += 1
        Loop

        Console.WriteLine()

        i = 0

        ' Equivalent Do While loop.
        Do While i < 10
            Console.WriteLine("Do While: {0}", i)
            i += 1
        Loop
    End Sub
End Module
Do Until: 0
Do Until: 1
Do Until: 2
Do Until: 3
Do Until: 4
Do Until: 5
Do Until: 6
Do Until: 7
Do Until: 8
Do Until: 9

Do While: 0
Do While: 1
Do While: 2
Do While: 3
Do While: 4
Do While: 5
Do While: 6
Do While: 7
Do While: 8
Do While: 9

Syntax

This syntax may be more readable if the terminating condition for the loop is the most intuitive. It really just depends on what you prefer.

Iteration

Iteration variables in the Do Until loop must be incremented with a separate statement. If you have an iteration variable (such as i) it is probably better to use a For-loop.

A review

Do Until may provide a clearer syntax for loops in some programs. For developers of languages based on C, though, the syntax may be less intuitive and worth avoiding.