Nested Loops in C (original) (raw)

Last Updated : 28 May, 2025

A nested loop means a loop statement inside another loop statement. That is why nested loops are also called "**loop inside loops". We can define any number of loops inside another loop.

For a nested loop, the inner loop performs all of its iterations for each iteration of the outer loop.

**Example: If the outer loop is running from i = 1 to 5 and the inner loop is running from a to e. Then, for each value of the outer loop variable (i), the inner loop will run from a to e.

Types of Nested Loops in C

We can create nested loops use any loop available in C language whether it be a for loop or a do while loop. We can also combine different type of loops to create nested loops.
Example: for loop inside a do while loop or a while loop in side a for loop etc.

1. Nested for Loop

Nested for loop refers to any type of loop that is defined inside a 'for' loop. Below is the equivalent flow diagram for nested 'for' loops:

Nested for loop in C

Flowchart for nested for loop in C

**Syntax:

C `

for ( initialization; condition; increment ) { for ( initialization; condition; increment ) { // statement of inside loop } // statement of outer loop }

`

**Example: Below program uses a nested for loop to print a 3D matrix of 2x3x2.

C `

#include <stdio.h>

int main() { // initializing the 3-D array int arr[2][3][2] = { { { 0, 6 }, { 1, 7 }, { 2, 8 } }, { { 3, 9 }, { 4, 10 }, { 5, 11 } } };

// Printing values of 3-D array
for (int i = 0; i < 2; ++i) {
    for (int j = 0; j < 3; ++j) {
        for (int k = 0; k < 2; ++k) {
            printf("Element at arr[%i][%i][%i] = %d\n",
                   i, j, k, arr[i][j][k]);
        }
    }
}
return 0;

}

`

Output

Element at arr[0][0][0] = 0 Element at arr[0][0][1] = 6 Element at arr[0][1][0] = 1 Element at arr[0][1][1] = 7 Element at arr[0][2][0] = 2 Element at arr[0][2][1] = 8 Element at arr[1][0][0] = 3 Element at arr[1][0][1] = 9 Element at arr[1][1][0] = 4 Element at arr[1][1][1] = 10 Element at arr[1][2][0] = 5 Element at arr[1][2][1] = 11

**2. Nested while Loop

A nested while loop refers to any type of loop that is defined inside a 'while' loop. Below is the equivalent flow diagram for nested 'while' loops:

Nested while loop in C

Flowchart for a nested while loop in C

**Syntax:

C `

while(condition) { while(condition) { // statement of inside loop } // statement of outer loop }

`

**Example: Print Pattern using nested while loops

C `

#include <stdio.h>

int main() { int end = 5;

printf("Pattern Printing using Nested While loop");

int i = 1;

while (i <= end) {
    printf("\n");
    int j = 1;
    while (j <= i) {
        printf("%d ", j);
        j = j + 1;
    }
    i = i + 1;
}
return 0;

}

`

Output

Pattern Printing using Nested While loop 1 1 2 1 2 3 1 2 3 4 1 2 3 4 5

3. Nested do-while Loop

A nested do-while loop refers to any type of loop that is defined inside a do-while loop. Below is the equivalent flow diagram for nested 'do-while' loops:

nested do while loop in C

flowchart for do while loop in C

**Syntax:

C `

do{ do{ // statement of inside loop }while(condition); // statement of outer loop }while(condition);

`

**Note: There is no rule that a loop must be nested inside its own type. In fact, there can be any type of loop nested inside any type and to any level.

**Syntax:

C `

do{ while(condition) { for ( initialization; condition; increment ) { // statement of inside for loop } // statement of inside while loop } // statement of outer do-while loop }while(condition);

`

**Example: Below program uses a nested for loop to print all prime factors of a number.

C `

#include <math.h> #include <stdio.h>

// A function to print all prime factors of a given number n void primeFactors(int n) { // Print the number of 2s that divide n while (n % 2 == 0) { printf("%d ", 2); n = n / 2; }

// n must be odd at this point. So we can skip
// one element (Note i = i +2)
for (int i = 3; i <= sqrt(n); i = i + 2) {
    // While i divides n, print i and divide n
    while (n % i == 0) {
        printf("%d ", i);
        n = n / i;
    }
}

// to handle the case when n
// is prime number greater than 2
if (n > 2)
    printf("%d ", n);

} int main() { int n = 315; primeFactors(n); return 0; }

`

Break Inside Nested Loops

Whenever we use a break statement inside the nested loops it breaks the innermost loop only and program control goes to the outer loop. Breaking the inner loop does not affects the outer loops.

**Example:

C `

#include <stdio.h>

int main() {

int i = 0;
for (int i = 0; i < 5; i++) {
    for (int j = 0; j < 3; j++) {
        // This inner loop will break when i==3
        if (i == 3) {
            break;
        }
        printf("* ");
    }
    printf("\n");
}
return 0;

}

`

Output

In the above program, the first loop will iterate from 0 to 5 but here if i will be equal to 3 it will break and will not print the * as shown in the output.

Continue Inside Nested loops

Whenever we use a continue statement inside the nested loops it skips the iteration of the innermost loop only. The outer loop remains unaffected.

**Example:

C `

#include <stdio.h>

int main() {

int i = 0;
for (int i = 0; i < 5; i++) {
    for (int j = 0; j < 3; j++) {
        // This inner loop will skip when j==2
        if (j==2) {
            continue;
        }
        printf("%d ",j);
    }
    printf("\n");
}
return 0;

}

`

In the above program, the inner loop will be skipped when j will be equal to 2. The outer loop will remain unaffected.

Uses of Nested Loops