Nested Loops

A nested loop is a loop placed inside another loop. The inner loop runs all its iterations for each single iteration of the outer loop.

This is commonly used for 2D arrays, matrices, and grid-based problems.

Execution flow:

Outer loop (row = 0) → Inner loop runs col = 0, 1, 2

Outer loop (row = 1) → Inner loop runs col = 0, 1, 2

Outer loop (row = 2) → Inner loop runs col = 0, 1, 2

Inner-loop bounds can depend on the outer index - useful for triangular patterns:

A practical use of nested loops is generating tables:

C++ stores multi-dimensional arrays in row-major order. Iterate rows in the outer loop and columns in the inner loop for better cache locality.

Keep the most frequently changing loop innermost for efficiency.

Avoid heavy calculations inside the innermost loop.

Prefer algorithms that reduce work (early exits, pruning) over micro-optimizations.