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Explaining the concepts of Label (break and continue) in Dart (#6451)
This PR improves the Dart documentation by adding detailed explanations and examples for the ```break``` and ```continue``` statements in various loop structures (for, while, do-while, and nested loops). The changes have made in two directories: 1) ```/examples/language/lib/control_flow/branches.dart``` 2) ```/src/content/language/branches.md``` Preview: https://dart-dev--pr6451-j-manoj-06-patch-4-fywn6bb1.web.app/language/loops#labels - [x] I’ve reviewed the contributor guide and applied the relevant portions to this PR. - [x] This PR doesn't contain automatically generated corrections or text (Grammarly, LLMs, and similar). - [x] This PR follows the [Google Developer Documentation Style Guidelines](https://developers.google.com/style) — for example, it doesn't use _i.e._ or _e.g._, and it avoids _I_ and _we_ (first person). - [x] This PR uses [semantic line breaks](https://github.com/dart-lang/site-shared/blob/main/doc/writing-for-dart-and-flutter-websites.md#semantic-line-breaks) of 80 characters or fewer. This ensures and follows the contributing guidelines. As per the issue , the Labels in Dart is explained with examples. Waiting for further improvements. Fixes #6289 Best regards, Manoj J --------- Co-authored-by: Amanda Fitch <18406675+antfitch@users.noreply.github.com> Co-authored-by: Parker Lougheed <parlough@gmail.com>
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‎examples/language/lib/control_flow/loops.dart‎

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@@ -74,4 +74,114 @@ void miscDeclAnalyzedButNotTested() {
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.forEach((c) => c.interview());
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// #enddocregion where
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}
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{
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// #docregion label-for-loop-break
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outerLoop:
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for (var i = 1; i <= 3; i++) {
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for (var j = 1; j <= 3; j++) {
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print('i = $i, j = $j');
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if (i == 2 && j == 2) {
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break outerLoop;
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}
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}
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}
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print('outerLoop exited');
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// #enddocregion label-for-loop-break
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}
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{
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// #docregion label-for-loop-continue
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outerLoop:
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for (var i = 1; i <= 3; i++) {
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for (var j = 1; j <= 3; j++) {
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if (i == 2 && j == 2) {
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continue outerLoop;
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}
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print('i = $i, j = $j');
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}
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}
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// #enddocregion label-for-loop-continue
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}
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{
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// #docregion label-while-loop-break
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var i = 1;
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outerLoop:
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while (i <= 3) {
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var j = 1;
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while (j <= 3) {
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print('i = $i, j = $j');
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if (i == 2 && j == 2) {
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break outerLoop;
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}
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j++;
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}
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i++;
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}
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print('outerLoop exited');
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// #enddocregion label-while-loop-break
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}
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{
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// #docregion label-while-loop-continue
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var i = 1;
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outerLoop:
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while (i <= 3) {
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var j = 1;
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while (j <= 3) {
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if (i == 2 && j == 2) {
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i++;
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continue outerLoop;
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}
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print('i = $i, j = $j');
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j++;
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}
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i++;
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}
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// #enddocregion label-while-loop-continue
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}
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{
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// #docregion label-do-while-loop-break
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var i = 1;
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outerLoop:
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do {
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var j = 1;
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do {
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print('i = $i, j = $j');
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if (i == 2 && j == 2) {
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break outerLoop;
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}
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j++;
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} while (j <= 3);
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i++;
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} while (i <= 3);
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print('outerLoop exited');
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// #enddocregion label-do-while-loop-break
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}
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{
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// #docregion label-do-while-loop-continue
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var i = 1;
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outerLoop:
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do {
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var j = 1;
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do {
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if (i == 2 && j == 2) {
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i++;
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continue outerLoop;
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}
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print('i = $i, j = $j');
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j++;
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} while (j <= 3);
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i++;
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} while (i <= 3);
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// #enddocregion label-do-while-loop-continue
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}
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}

‎src/content/language/loops.md‎

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@@ -142,6 +142,237 @@ candidates
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.forEach((c) => c.interview());
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```
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## Labels
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A label is an identifier followed by a colon (`labelName:`)
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that you can place before a statement to create a
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_labeled statement_. Loops and switch cases are often used as
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labeled statements. A labeled statement can be referenced later
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in a `break` or `continue` statement as follows:
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* `break labelName;`
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Terminates the execution of the labeled statement.
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This is useful for breaking out of a specific outer loop when you're
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within a nested loop.
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* `continue labelName;`
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Skips the rest of the current iteration of the
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labeled statement loop and continues with the next iteration.
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Labels are used to manage control flow. They are often used with
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loops and switch cases and allow you to specify which statement to
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break out of or continue, rather than affecting the innermost
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loop by default.
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### Labels in for loop using `break` {:.no_toc}
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The following code demonstrates the usage of a label called `outerLoop`
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in a `for` loop with a `break` statement:
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<?code-excerpt "language/lib/control_flow/loops.dart (label-for-loop-break)"?>
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```dart
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outerLoop:
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for (var i = 1; i <= 3; i++) {
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for (var j = 1; j <= 3; j++) {
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print('i = $i, j = $j');
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if (i == 2 && j == 2) {
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break outerLoop;
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}
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}
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}
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print('outerLoop exited');
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```
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In the previous example, when `i == 2` and `j == 2`, the `break outerLoop;`
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statement stops both inner and outer loops. As a result, the output is:
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```plaintext
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i = 1, j = 1
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i = 1, j = 2
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i = 1, j = 3
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i = 2, j = 1
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i = 2, j = 2
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outerLoop exited
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```
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### Labels in for loop using `continue` {:.no_toc}
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The following code demonstrates the use of a label called `outerLoop`
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in a `for` loop with a `continue` statement:
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<?code-excerpt "language/lib/control_flow/loops.dart (label-for-loop-continue)"?>
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```dart
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outerLoop:
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for (var i = 1; i <= 3; i++) {
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for (var j = 1; j <= 3; j++) {
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if (i == 2 && j == 2) {
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continue outerLoop;
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}
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print('i = $i, j = $j');
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}
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}
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```
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In the previous example, when `i == 2` and `j == 2`, `continue outerLoop;` skips the
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rest of the iterations for `i = 2` and moves to `i = 3`. As a result, the output is:
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```plaintext
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i = 1, j = 1
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i = 1, j = 2
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i = 1, j = 3
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i = 2, j = 1
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i = 3, j = 1
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i = 3, j = 2
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i = 3, j = 3
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```
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### Labels in while loop using `break` {:.no_toc}
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The following code demonstrates the use of a label called `outerLoop` in
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a `while` loop with a `break` statement:
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<?code-excerpt "language/lib/control_flow/loops.dart (label-while-loop-break)"?>
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```dart
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var i = 1;
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outerLoop:
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while (i <= 3) {
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var j = 1;
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while (j <= 3) {
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print('i = $i, j = $j');
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if (i == 2 && j == 2) {
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break outerLoop;
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}
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j++;
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}
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i++;
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}
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print('outerLoop exited');
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```
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In the previous example, the program breaks out of both inner and outer `while` loops
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when `i == 2` and `j == 2`. As a result, the output is:
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```plaintext
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i = 1, j = 1
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i = 1, j = 2
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i = 1, j = 3
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i = 2, j = 1
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i = 2, j = 2
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outerLoop exited
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```
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### Labels in while loop using `continue` {:.no_toc}
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The following code demonstrates the use of a label called `outerLoop` in
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a `while` loop with a `continue` statement:
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<?code-excerpt "language/lib/control_flow/loops.dart (label-while-loop-continue)"?>
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```dart
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var i = 1;
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outerLoop:
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while (i <= 3) {
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var j = 1;
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while (j <= 3) {
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if (i == 2 && j == 2) {
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i++;
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continue outerLoop;
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}
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print('i = $i, j = $j');
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j++;
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}
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i++;
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}
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```
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In the previous example, the iteration for `i = 2` and `j = 2` is skipped and the loop moves
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directly to `i = 3`. As a result, the output is:
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```plaintext
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i = 1, j = 1
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i = 1, j = 2
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i = 1, j = 3
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i = 2, j = 1
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i = 3, j = 1
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i = 3, j = 2
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i = 3, j = 3
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```
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### Labels in do-while loop using `break` {:.no_toc}
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The following code demonstrates the use of a label called `outerLoop` in
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a `do while` loop with a `break` statement:
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<?code-excerpt "language/lib/control_flow/loops.dart (label-do-while-loop-break)"?>
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```dart
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var i = 1;
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outerLoop:
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do {
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var j = 1;
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do {
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print('i = $i, j = $j');
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if (i == 2 && j == 2) {
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break outerLoop;
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}
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j++;
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} while (j <= 3);
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i++;
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} while (i <= 3);
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print('outerLoop exited');
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```
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In the previous example, the program breaks out of both inner and outer loops when `i == 2` and
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`j == 2`. As a result, the output is:
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```plaintext
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i = 1, j = 1
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i = 1, j = 2
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i = 1, j = 3
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i = 2, j = 1
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i = 2, j = 2
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outerLoop exited
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```
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### Labels in do-while loop using `continue` {:.no_toc}
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The following code demonstrates the use of a label called `outerLoop` in
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a `do while` loop with a `continue` statement:
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<?code-excerpt "language/lib/control_flow/loops.dart (label-do-while-loop-continue)"?>
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```dart
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var i = 1;
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outerLoop:
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do {
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var j = 1;
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do {
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if (i == 2 && j == 2) {
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i++;
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continue outerLoop;
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}
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print('i = $i, j = $j');
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j++;
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} while (j <= 3);
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i++;
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} while (i <= 3);
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```
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In the previous example, the loop skips `i = 2` and `j = 2` and moves directly to `i = 3`.
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As a result, the output is:
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```plaintext
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i = 1, j = 1
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i = 1, j = 2
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i = 1, j = 3
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i = 2, j = 1
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i = 3, j = 1
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i = 3, j = 2
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i = 3, j = 3
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```
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[exceptions]: /language/error-handling
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[branching]: /language/branches
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[iteration]: /libraries/dart-core#iteration

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