Nested loop

Nested loop

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

Syntax

 The syntax for a nested for loop statement in C++ is as follows:

 statement in switch case. See the example below:

for ( init; condition; increment ) 

{

          for ( init; condition; increment ) 

{

             statement(s);

} 

          statement(s);             // you can put more statements.

}

The syntax for a nested while loop statement in C++ is as follows:

while(condition) 

{

while(condition) 

{

statement(s);

}

   statement(s);         // you can put more statements.


}

The syntax for a nested do...while loop statement in C++ is as follows: 

          for ( init; condition; increment ) 

{

             statement(s);

} 

          statement(s);             // you can put more statements.

}

The syntax for a nested while loop statement in C++ is as follows:

do {

statement(s); // you can put more statements. do {

statement(s); 

}

while( condition ); 

}

while( condition );

Example 

The following program uses a nested for loop to find the prime numbers from 2 to 100:

#include <iostream> 

using namespace std;

int main () 

{

int i, j;

for(i=2; i<100; i++)

 { 

    for(j=2; j <= (i/j); j++)

        if(!(i%j)) 

         break; // if factor found, not prime 

      if(j > (i/j))

    cout << i << " is prime\n";

} return 0;

} 

This would produce the following result:

2 is prime

 3 is prime 

5 is prime

 7 is prime

 11 is prime 

13 is prime 

17 is prime

 19 is prime

 23 is prime 

29 is prime 

31 is prime 

37 is prime 

41 is prime

 43 is prime 

47 is prime

 53 is prime 

59 is prime 

61 is prime 

67 is prime 

71 is prime 

73 is prime 

79 is prime 

83 is prime 

89 is prime 

97 is prime