Control Flow

Break and Continue

continue and break change a loop's normal flow. continue skips the rest of the current iteration and resumes at the next condition check (plus the for step if any). break exits the loop immediately, ignoring later iterations entirely. Both are useful for guarding the body's happy path and for bailing out as soon as a stop condition is met.

Program

Play the program to loop over 1..5, continue on 2, break on 5, and keep [1, 3, 4].

break_continue.dart
Replay: real traced execution (multi-file project)
void main() {
  var kept = <int>[];
  for (var n = 1; n <= 5; n++) {
    if (n == 2) continue;
    if (n == 5) break;
    kept.add(n);
  }
  var summary = kept.join(',');
  print('kept=$summary');
}

  1. kept ← []

    1void main() {2  var kept = <int>[];3  for (var n = 1; n <= 5; n++) {
    values this step[]kept

  2. n ← 1

    2var kept = <int>[];3for (var n = 1; n <= 5; n++) {4  if (n == 2) continue;
    values this step1n

  3. kept ← [1]

    5  if (n == 5) break;6  kept.add(n);7}
    values this step[] → [1]kept1n

  4. n ← 2

    2var kept = <int>[];3for (var n = 1; n <= 5; n++) {4  if (n == 2) continue;
    values this step2n

  5. continue at ← n == 2

    3for (var n = 1; n <= 5; n++) {4  if (n == 2) continue;5  if (n == 5) break;
    values this stepn == 2continue at2n

  6. n ← 3

    2var kept = <int>[];3for (var n = 1; n <= 5; n++) {4  if (n == 2) continue;
    values this step3n

  7. kept ← [1, 3]

    5  if (n == 5) break;6  kept.add(n);7}
    values this step[1] → [1, 3]kept3n

  8. n ← 4

    2var kept = <int>[];3for (var n = 1; n <= 5; n++) {4  if (n == 2) continue;
    values this step4n

  9. kept ← [1, 3, 4]

    5  if (n == 5) break;6  kept.add(n);7}
    values this step[1, 3] → [1, 3, 4]kept4n

  10. n ← 5

    2var kept = <int>[];3for (var n = 1; n <= 5; n++) {4  if (n == 2) continue;
    values this step5n

  11. break at ← n == 5

    4if (n == 2) continue;5if (n == 5) break;6kept.add(n);
    values this stepn == 5break at5n

  12. summary ← 1,3,4

    7}8var summary = kept.join(',');9print('kept=$summary');
    values this step1,3,4summary[1, 3, 4]kept

  13. print('kept=$summary');

    8  var summary = kept.join(',');9  print('kept=$summary');10}
    outputkept=1,3,4
    values this step1,3,4summary

Skip Two, Stop at Five

  1. kept starts empty.
  2. The loop visits 1, 2, 3, 4, and 5.
  3. 2 uses continue, so it is skipped.
  4. 5 uses break, so the loop stops.
  5. The program prints kept=1,3,4. | n | Action | Kept values | | --- | --- | --- | | 1 | add | 1 | | 2 | continue | 1 | | 3 | add | 1,3 | | 4 | add | 1,3,4 | | 5 | break | 1,3,4 |
continue `continue` skips the rest of the current iteration and jumps to the next condition check (and the `for` step). The body's later statements are not run for that iteration.
break `break` exits the loop immediately. No condition check, no increment step, no remaining iterations.
guard before work Putting `continue`/`break` early keeps the rest of the body as the normal happy path. The loop ran for `n = 1..5` but only added `1, 3, 4` because `2` was skipped and `5` triggered exit.

Exercise: break_continue.dart

Use continue to skip 2, break at 5, and print kept=1,3,4