carbon-lang/docs/design/control_flow/loops.md

Loops

Table of contents

• while
• for
• break
• continue
• Relevant proposals

while

while statements loop for as long as the passed expression returns True. For example, this prints 0, 1, 2, then Done!:

var x: Int = 0;
while (x < 3) {
  Print(x);
  ++x;
}
Print("Done!");

TODO: Flesh out text (currently just overview)

for

for statements support range-based looping, typically over containers. For example, this prints all names in names:

for (var name: String in names) {
  Print(name);
}

PrintNames() prints each String in the names List in iteration order.

TODO: Flesh out text (currently just overview)

break

The break statement immediately ends a while or for loop. Execution will resume at the end of the loop's scope. For example, this processes steps until a manual step is hit (if no manual step is hit, all steps are processed):

for (var step: Step in steps) {
  if (step.IsManual()) {
    Print("Reached manual step!");
    break;
  }
  step.Process();
}

TODO: Flesh out text (currently just overview)

continue

The continue statement immediately goes to the next loop of a while or for. In a while, execution continues with the while expression. For example, this prints all non-empty lines of a file, using continue to skip empty lines:

var f: File = OpenFile(path);
while (!f.EOF()) {
  var line: String = f.ReadLine();
  if (line.IsEmpty()) {
    continue;
  }
  Print(line);
}

TODO: Flesh out text (currently just overview)

Relevant proposals

Most discussion of design choices and alternatives may be found in relevant proposals.

• while
• for