FreeBasic Do Loop Keywords

last modified June 16, 2025

The FreeBasic Do and Loop keywords create loops that repeat a block of code. They offer flexible control structures with different condition checking positions.

Basic Definition

In FreeBasic, Do and Loop work together to create looping structures. The loop continues until a specified condition is met.

There are four main variations: Do While, Do Until, Loop While, and Loop Until. Each checks the condition at different points in the loop execution.

Basic Do Loop

This example shows the simplest infinite loop structure using Do/Loop.

basic_do_loop.bas

Dim counter As Integer = 0

Do
    counter += 1
    Print "Counter: "; counter
    
    If counter >= 5 Then
        Exit Do
    End If
Loop

Print "Loop ended"

This creates an infinite loop that increments a counter. The Exit Do statement breaks the loop when counter reaches 5. Without Exit Do, this loop would run indefinitely.

Do While Loop

The Do While loop checks the condition before each iteration.

do_while_loop.bas

Dim number As Integer = 1

Do While number <= 10
    Print "Number: "; number
    number += 2
Loop

Print "Loop completed"

This loop prints odd numbers from 1 to 10. The condition is checked before each iteration. If false initially, the loop body never executes. The variable is modified inside the loop to eventually make the condition false.

Do Until Loop

The Do Until loop runs until the condition becomes true.

do_until_loop.bas

Dim password As String
Dim attempts As Integer = 0

Do Until password = "secret" Or attempts >= 3
    Input "Enter password: ", password
    attempts += 1
Loop

If password = "secret" Then
    Print "Access granted"
Else
    Print "Too many attempts"
End If

This loop prompts for a password until either the correct password is entered or 3 attempts are made. Unlike While, Until continues until the condition becomes true rather than while it remains true.

Loop While

The Loop While checks the condition after each iteration.

loop_while.bas

Dim response As String

Do
    Input "Do you want to continue (yes/no)? ", response
    response = LCase(response)
Loop While response = "yes"

Print "Goodbye"

This loop always executes at least once before checking the condition. It continues while the user enters "yes". The condition is evaluated after each complete iteration of the loop body.

Loop Until

The Loop Until checks its condition after each iteration.

loop_until.bas

Dim randomNum As Integer
Dim guess As Integer
Dim tries As Integer = 0

Randomize Timer
randomNum = Int(Rnd * 10) + 1

Do
    Input "Guess the number (1-10): ", guess
    tries += 1
    
    If guess < randomNum Then
        Print "Too low"
    ElseIf guess > randomNum Then
        Print "Too high"
    End If
Loop Until guess = randomNum

Print "Correct! You guessed it in "; tries; " tries"

This number guessing game loop runs until the correct number is guessed. The condition is checked after each attempt. The loop always runs at least once before checking the exit condition.

Nested Do Loops

Do loops can be nested inside other Do loops for complex logic.

nested_loops.bas

Dim i As Integer = 1

Do While i <= 3
    Dim j As Integer = 1
    
    Do While j <= 3
        Print "i:"; i; " j:"; j
        j += 1
    Loop
    
    i += 1
Loop

Print "Nested loops completed"

This example shows two nested Do While loops. The outer loop runs 3 times, and for each outer iteration, the inner loop runs 3 times. This creates a total of 9 iterations (3×3) of the inner loop's body.

Do Loop With Continue

The Continue Do statement skips the rest of the current iteration.

continue_do.bas

Dim n As Integer = 0

Do While n < 10
    n += 1
    
    If n Mod 2 = 0 Then
        Continue Do
    End If
    
    Print "Odd number: "; n
Loop

Print "Finished"

This loop prints only odd numbers between 1 and 10. When an even number is encountered, Continue Do skips the print statement and jumps to the next iteration. The loop condition is still checked normally.

Best Practices

Initialization: Always initialize loop control variables before the loop.
Termination: Ensure the loop has a clear exit condition.
Readability: Prefer While/Until conditions over Exit Do when possible.
Performance: Move invariant calculations outside loops.
Indentation: Consistently indent loop bodies for clarity.

This tutorial covered FreeBasic's Do and Loop keywords with practical examples showing different looping structures.

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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