C Nested Loops

A nested loop in C is a loop inside another loop. This allows you to iterate over multiple dimensions or perform more complex iterations. The inner loop runs completely for each iteration of the outer loop.

1. Nested Loop Syntax

In C, you can place a loop (either a for, while, or do-while loop) inside another loop. The outer loop runs once for each iteration of the inner loop.

                        
for (initialization; condition; increment) {
    for (initialization; condition; increment) {
    // Inner loop statements
    }
}
                        
                    

                        
#include <stdio.h>
int main() 
{
    for (int i = 0; i < 3; i++) {
    or (int j = 0; j < 3; j++) {
    printf("i = %d, j = %d\n", i, j);
    }
    }
    return 0;
}
             
                 
                    

2. Key Points of Nested Loops

• The inner loop executes completely for each iteration of the outer loop.
• Nested loops can be of any type: for, while, or do-while.
• Be cautious when using nested loops, as they can lead to performance issues if the number of iterations grows large.

3. When to Use Nested Loops

• Use nested loops when you need to perform iterations over multiple dimensions or levels, such as when working with matrices or grids.
• They are also useful when you need to perform repetitive actions in a set of data structures, like iterating over arrays of arrays.

4. Example of Nested Loops in Arrays

Nested loops are often used with multidimensional arrays. For example, a 2D array can be iterated using nested loops.

                        
#include <stdio.h>
int main() 
{
  int arr[3][3] = {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
    };
        
    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%d ", arr[i][j]);
        }
        printf("\n");
    }
        return 0;
}
                        
                    

5. Key Considerations

• The time complexity of a nested loop is multiplied by the number of iterations of each loop. For example, a loop with 3 iterations and a nested loop with 3 iterations has a time complexity of O(3 * 3) = O(9).
• Be cautious with deeply nested loops (loops inside loops inside loops), as they can cause performance issues if not managed properly.

6. Nested `do-while` Loop

A nested `do-while` loop is similar to a regular `do-while` loop but can execute its statements multiple times for each iteration of the outer loop. It ensures that the loop's body executes at least once before checking the condition.

                        
#include <stdio.h>
int main() 
{
   int i = 0, j = 0;
   do {
        j = 0;
        do {
            printf("i = %d, j = %d\n", i, j);
            j++;
        } while (j < 3);
        i++;
     } while (i < 3);
     return 0;
}
                        
                    

7. Nested `while` Loop

A nested `while` loop is another variation where the inner loop is controlled using a `while` loop instead of a `for` loop. It can be used when you want more flexibility in controlling the number of iterations of the inner loop.

                        
#include <stdio.h>
int main() 
{
  int i = 0, j = 0;
  while (i < 3) {
        j = 0;
        while (j < 3)
        {
        printf("i = %d, j = %d\n", i, j);
        j++;
        }
          i++;
}
    return 0;
}