Nested Loops in Dart

What are Nested Loops?

A nested loop is a loop inside another loop. For each iteration of the outer loop, the inner loop completes all its iterations. They are commonly used for working with 2D data like grids, matrices, and patterns.

Example

void main() {
  // Multiplication table (3x3)
  for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 3; j++) {
      print('$i x $j = $${i * j}');
    }
  }
}

1 x 1 = 1
1 x 2 = 2
1 x 3 = 3
2 x 1 = 2
...
3 x 3 = 9

Printing Patterns

// Right triangle of stars
for (int i = 1; i <= 5; i++) {
  String row = '';
  for (int j = 1; j <= i; j++) {
    row += '* ';
  }
  print(row);
}

*
* *
* * *
* * * *
* * * * *

⚠️ Performance Note

Nested loops multiply execution time. A 3-level loop over N items runs N³ times. Keep nesting to a minimum and consider algorithmic alternatives for large datasets.

🧠 Quiz

Summary

Nested loops place one loop inside another. For each outer iteration, the inner loop completes fully. Use them for grids, patterns, and 2D data. Be mindful of the O(n²) or higher time complexity they introduce.