FreeBasic Loop Until Keyword

last modified June 21, 2025

The FreeBasic Loop Until statement creates a loop that continues executing until a specified condition becomes true. Unlike While loops, it always executes at least once before checking the condition.

Basic Definition

In FreeBasic, Loop Until is a post-test loop structure. The loop body executes first, then the condition is evaluated. If false, the loop repeats. The syntax is simple: Do ... Loop Until condition.

This loop is ideal when you need to execute code at least once before checking a termination condition. It's commonly used for input validation and menu systems where initial execution is required.

Simple Loop Until Example

This basic example demonstrates the fundamental structure of a Loop Until.

loop_until_basic.bas

Dim counter As Integer = 1

Do
    Print "Iteration: "; counter
    counter += 1
Loop Until counter > 5

The loop prints numbers from 1 to 5. It increments the counter each iteration and checks if it exceeds 5. Note that the condition is evaluated after the loop body executes, ensuring at least one iteration.

Input Validation with Loop Until

Loop Until can be used for validating user input, as it ensures at least one prompt is displayed.

loop_until_input.bas

Dim age As Integer

Do
    Input "Enter your age (18+): ", age
Loop Until age >= 18

Print "Valid age entered: "; age

This code repeatedly asks for age until a value of 18 or more is entered. The loop guarantees the prompt appears at least once, making it ideal for user input scenarios where initial interaction is required.

Loop Until with Boolean Flag

Using a Boolean flag with Loop Until provides clear loop control.

loop_until_flag.bas

Randomize Timer  ' Seed the random number generator

Dim isDone As Boolean = False
Dim randomValue As Integer = 0

Do
    randomValue = Int(Rnd * 30) + 1
    Print "Random value: "; randomValue
    
    If randomValue = 22 Then
        isDone = True
    End If
Loop Until isDone

Here we use a Boolean flag to control the loop. The loop continues until the random value equals 22. The flag isDone is set to when the condition is met, allowing for clear and explicit loop termination.

Nested Loop Until

Loop Until statements can be nested to create complex control structures.

loop_until_nested.bas

Dim outer As Integer = 1
Dim inner As Integer

Do
    inner = 1
    Print "Outer loop: "; outer
    
    Do
        Print "  Inner loop: "; inner
        inner += 1
    Loop Until inner > 3
    
    outer += 1
Loop Until outer > 4

This example shows nested Loop Until structures. The inner loop completes all its iterations for each outer loop iteration. Nested loops are useful for working with multi-dimensional data or complex algorithms.

Loop Until with Array Processing

Loop Until can process arrays until a condition is met.

loop_until_array.bas

Dim numbers(1 To 5) As Integer = {10, 20, 30, 40, 50}
Dim index As Integer = 1
Dim sum As Integer = 0

Do
    sum += numbers(index)
    index += 1
Loop Until index > 5 Or sum > 75

Print "Sum: "; sum
Print "Processed elements: "; index - 1

This code sums array elements until either all elements are processed or the sum exceeds 75. The compound condition demonstrates how Loop Until can handle multiple exit criteria. The loop stops when either condition becomes true.

Loop Until with Random Numbers

Loop Until works well with random number generation scenarios.

loop_until_random.bas

Randomize Timer
Dim target As Integer = 50
Dim attempts As Integer = 0
Dim guess As Integer

Do
    guess = Int(Rnd * 100) + 1
    attempts += 1
    Print "Attempt "; attempts; ": "; guess
Loop Until guess = target

Print "Found "; target; " in "; attempts; " attempts"

This example generates random numbers until the target value (50) is found. The loop continues until the random number matches the target, counting each attempt. This demonstrates Loop Until's usefulness in probabilistic scenarios.

Loop Until with Early Exit

The Exit Do statement can provide early termination within a Loop Until.

loop_until_exit.bas

#include "vbcompat.bi"

Dim today As String = Format(Now, "dddd")
Dim guess As String
Dim attempts As Integer = 0
Dim correct As Boolean = False

Do
    Input "Guess today's date: ", guess

    If guess = today Then
        correct = True
        Exit Do
    End If

    attempts += 1
    If attempts >= 3 Then
        Exit Do
    End If
Loop

If correct Then
    Print "Correct! Today is "; today
Else
    Print "Out of attempts! The correct date was "; today
End If

This password checker uses Loop Until with an early exit condition. If three incorrect attempts occur, the loop exits immediately using Exit Do. Otherwise, it continues until the correct password is entered.

Best Practices

Readability: Keep loop conditions simple and clear.
Initialization: Initialize variables before the loop.
Termination: Ensure the loop can eventually terminate.
Complexity: Avoid deeply nested Loop Until structures.
Comments: Document non-obvious loop conditions.

This tutorial covered the FreeBasic Loop Until keyword with practical examples showing its usage in different scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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