Explain concept of nested loops with examples

Nested loops are a concept in programming where a loop is placed inside another loop. This is often used when dealing with multi-dimensional data structures like arrays or matrices, where each element needs to be processed.

Here's a simple example in Python:

for i in range(3):  # outer loop
    for j in range(3):  # inner loop
        print(i, j)

In this example, for each iteration of the outer loop (i), the inner loop (j) runs completely. So for i=0, j will run for values 0, 1, and 2. Then i will increment to 1, and again j will run for values 0, 1, and 2. This will continue until i has run for all its values.

The output of this program will be:

0 0
0 1
0 2
1 0
1 1
1 2
2 0
2 1
2 2

This shows that every possible combination of i and j is printed, which is the result of the nested loop structure.