Writing a loop inside another loop is known as nested loop. Maximum level of nesting allowed in C++ is 256. We can write `while`

, `do...while`

, `for`

and range based for loop in a nested loop.

## Nested While Loop

The syntax of nested while loop is shown below

while (expression) { while (expression) { statement(s) } statement(s) }

Below is an example of nested while loop

#include <iostream> using namespace std; int main () { int i = 0; while(i < 3) { int j = 0; while(j < 5) { cout << "i = " << i << " and j = " << j << endl; j++; } i++; } return 0; }

Below is the output of above program

i = 0 and j = 0

i = 0 and j = 1

i = 0 and j = 2

i = 0 and j = 3

i = 0 and j = 4

i = 1 and j = 0

i = 1 and j = 1

i = 1 and j = 2

i = 1 and j = 3

i = 1 and j = 4

i = 2 and j = 0

i = 2 and j = 1

i = 2 and j = 2

i = 2 and j = 3

i = 2 and j = 4

## Nested Do-While Loop

The syntax of nested do…while loop is shown below

do { do { statement(s) }while (expression) statement(s) }while (expression)

Below is an example of nested do…while loop

#include <iostream> using namespace std; int main () { int i = 0; do { int j = 0; do { cout << "i = " << i << " and j = " << j << endl; j++; }while(j < 5); i++; }while(i < 3); return 0; }

Below is the output of above program

i = 0 and j = 0

i = 0 and j = 1

i = 0 and j = 2

i = 0 and j = 3

i = 0 and j = 4

i = 1 and j = 0

i = 1 and j = 1

i = 1 and j = 2

i = 1 and j = 3

i = 1 and j = 4

i = 2 and j = 0

i = 2 and j = 1

i = 2 and j = 2

i = 2 and j = 3

i = 2 and j = 4

## Nested For Loop

The syntax of nested for loop is shown below

for (initialization; termination; increment-decrement) { for (initialization; termination; increment-decrement) { statement(s) } statement(s) }

Below is an example of nested for loop

#include <iostream> using namespace std; int main () { for(int i = 0; i < 3; i++) { int j = 0; for(int j = 0; j < 5; j++) { cout << "i = " << i << " and j = " << j << endl; } } return 0; }

Below is the output of above program

i = 0 and j = 0

i = 0 and j = 1

i = 0 and j = 2

i = 0 and j = 3

i = 0 and j = 4

i = 1 and j = 0

i = 1 and j = 1

i = 1 and j = 2

i = 1 and j = 3

i = 1 and j = 4

i = 2 and j = 0

i = 2 and j = 1

i = 2 and j = 2

i = 2 and j = 3

i = 2 and j = 4

## Nested Range-Based For Loop

The syntax of nested range-based for loop is shown below

for ( range_declaration : range_expression ) { for ( range_declaration : range_expression ) { statement(s); } statement(s); }

Below is an example of nested for loop

#include <iostream> using namespace std; int main () { int arr1[3] = {0,1,2}; int arr2[5] = {0,1,2,3,4}; for(int i : arr1) { for(int j : arr2) { cout << "i = " << i << " and j = " << j << endl; } } return 0; }

Below is the output of above program

i = 0 and j = 1

i = 0 and j = 2

i = 0 and j = 3

i = 0 and j = 4

i = 1 and j = 0

i = 1 and j = 1

i = 1 and j = 2

i = 1 and j = 3

i = 1 and j = 4

i = 2 and j = 0

i = 2 and j = 1

i = 2 and j = 2

i = 2 and j = 3

i = 2 and j = 4