C++ `Nested Loops`

A loop can be nested inside another loop. C++ allows at least 256 levels of nesting.

Syntax

The syntax for nested for loops in C++:

for ( init; condition; increment )
{
   for ( init; condition; increment )
   {
      statement(s);
   }
   statement(s); // More statements can be placed here
}

The syntax for nested while loops in C++:

while(condition)
{
   while(condition)
   {
      statement(s);
   }
   statement(s); // More statements can be placed here
}

The syntax for nested do...while loops in C++:

do
{
   statement(s); // More statements can be placed here
   do
   {
      statement(s);
   } while( condition );

} while( condition );

It's worth noting that you can nest any type of loop within any other type of loop. For example, a for loop can be nested inside a while loop, and vice versa.

Example

The following program uses a nested for loop to find prime numbers between 2 and 100:

#include <iostream>
using namespace std;

int main ()
{
    int i, j;
    for(i=2; i&lt;100; i++) {
        for(j=2; j <= (i/j); j++) {
            if(!(i%j)) {
                break; // If a factor is found, it's not a prime
            }
        }
        if(j > (i/j)) {
            cout << i << " is a prime number\n";
        }
    }
    return 0;
}

When the above code is compiled and executed, it produces the following result:

2 is a prime number
3 is a prime number
5 is a prime number
7 is a prime number
11 is a prime number
13 is a prime number
17 is a prime number
19 is a prime number
23 is a prime number
29 is a prime number
31 is a prime number
37 is a prime number
41 is a prime number
43 is a prime number
47 is a prime number
53 is a prime number
59 is a prime number
61 is a prime number
67 is a prime number
71 is a prime number
73 is a prime number
79 is a prime number
83 is a prime number
89 is a prime number
97 is a prime number

C++ Loops

❮ Cpp Null Pointers Cpp Pointers ❯

C++ Nested Loops

Syntax

Example

C++ `Nested Loops`