# Loops DWScript supports the standard Pascal loops: `for`, `while`, and `repeat`. ## For Loop The `for` loop is ideal when the number of iterations is known in advance. ```pascal // Standard counting up for var i := 1 to 5 do PrintLn('Count: ' + i.ToString); // Counting down for var j := 10 downto 1 do PrintLn('Countdown: ' + j.ToString); // OUTPUT // Count: 1 // Count: 2 // Count: 3 // Count: 4 // Count: 5 // Countdown: 10 // Countdown: 9 // Countdown: 8 // Countdown: 7 // Countdown: 6 // Countdown: 5 // Countdown: 4 // Countdown: 3 // Countdown: 2 // Countdown: 1 ``` ### Step Clause DWScript extends the standard `for` loop with an optional `step` clause. Note that the **step value must always be positive**, even when counting down with `downto`. ```pascal // Count by 2 for var i := 0 to 10 step 2 do Print(i.ToString + ' '); PrintLn(''); // Count down by 2 (Step is still positive) for var j := 10 downto 0 step 2 do Print(j.ToString + ' '); // OUTPUT // 0 2 4 6 8 10 // 10 8 6 4 2 0 ``` ## Variable Scope & Values DWScript handles loop variables with predictable scoping and post-loop values. ### Inline Scope When using `for var i := ...`, the variable `i` is scoped **only to the loop body**. It is not accessible after the loop. ### Post-Loop Values When using a pre-declared variable, its value after the loop is **well-defined**. It will be the first value that failed the loop condition (unlike Delphi, where the value is considered undefined). ```pascal var k: Integer; for k := 1 to 3 do begin // Loop body end; // k is now 4 (the value that broke the 'k <= 3' condition) PrintLn('k after loop: ' + k.ToString); // OUTPUT // k after loop: 4 ``` ## While Loop The `while` loop checks the condition *before* each iteration. It may run zero times if the condition is initially false. ```pascal var n := 0; while n < 3 do begin PrintLn('Running: ' + n.ToString); Inc(n); end; // OUTPUT // Running: 0 // Running: 1 // Running: 2 ``` ## Repeat Loop The `repeat` loop checks the condition *after* each iteration. It is guaranteed to run **at least once**. ```pascal var i := 0; repeat PrintLn('Value: ' + i.ToString); Inc(i); until i > 2; // OUTPUT // Value: 0 // Value: 1 // Value: 2 ``` ## Loop Control You can modify the execution flow within any loop using jump statements: * **[break](/lang/control_flow/jumps)**: Terminate the loop immediately. * **[continue](/lang/control_flow/jumps)**: Skip to the next iteration. :::info For iterating over collections like arrays, sets, or strings, use the more modern **[for..in iteration](/lang/control_flow/iteration)**. :::

Loops

DWScript supports the standard Pascal loops: for, while, and repeat.

For Loop

The for loop is ideal when the number of iterations is known in advance.

// Standard counting up
for var i := 1 to 5 do
  PrintLn('Count: ' + i.ToString);

// Counting down
for var j := 10 downto 1 do
  PrintLn('Countdown: ' + j.ToString);

Result

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5
Countdown: 10
Countdown: 9
Countdown: 8
Countdown: 7
Countdown: 6
Countdown: 5
Countdown: 4
Countdown: 3
Countdown: 2
Countdown: 1

Step Clause

DWScript extends the standard for loop with an optional step clause. Note that the step value must always be positive, even when counting down with downto.

// Count by 2
for var i := 0 to 10 step 2 do
  Print(i.ToString + ' ');

PrintLn('');

// Count down by 2 (Step is still positive)
for var j := 10 downto 0 step 2 do
  Print(j.ToString + ' ');

Result

0 2 4 6 8 10 
10 8 6 4 2 0

Variable Scope & Values

DWScript handles loop variables with predictable scoping and post-loop values.

Inline Scope

When using for var i := ..., the variable i is scoped only to the loop body. It is not accessible after the loop.

Post-Loop Values

When using a pre-declared variable, its value after the loop is well-defined. It will be the first value that failed the loop condition (unlike Delphi, where the value is considered undefined).

var k: Integer;
for k := 1 to 3 do begin
  // Loop body
end;

// k is now 4 (the value that broke the 'k <= 3' condition)
PrintLn('k after loop: ' + k.ToString);

Result

k after loop: 4

While Loop

The while loop checks the condition before each iteration. It may run zero times if the condition is initially false.

var n := 0;
while n < 3 do begin
  PrintLn('Running: ' + n.ToString);
  Inc(n);
end;

Result

Running: 0
Running: 1
Running: 2

Repeat Loop

The repeat loop checks the condition after each iteration. It is guaranteed to run at least once.

var i := 0;
repeat
  PrintLn('Value: ' + i.ToString);
  Inc(i);
until i > 2;

Result

Value: 0
Value: 1
Value: 2

Loop Control

You can modify the execution flow within any loop using jump statements:

break: Terminate the loop immediately.
continue: Skip to the next iteration.

For iterating over collections like arrays, sets, or strings, use the more modern for..in iteration.

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