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

#include <stdio.h>

int main()
{
    int i, j;

    for (i = 1; i <= 3; i++)
    {
        for (j = 1; j <= 2; j++)
        {
            printf("i = %d, j = %d\n", i, j);
        }
    }

    return 0;
}

Example Output #

i = 1, j = 1
i = 1, j = 2
i = 2, j = 1
i = 2, j = 2
i = 3, j = 1
i = 3, j = 2

Explanation #

The outer loop controls i:

for (i = 1; i <= 3; i++)

For each value of i, the inner loop runs completely:

for (j = 1; j <= 2; j++)

When i is 1, the inner loop runs with j equal to 1 and 2. The same process occurs for i values 2 and 3.

Therefore, the inner loop executes 2 times for each of the 3 outer-loop iterations, resulting in a total of 6 executions of the printf() statement.