/* This program prints all positive prime integers less than or
     equal to the user-supplied value n.                           */
     
     #include <stdio.h>
     
     main()
     {
          int possible_prime, n, possible_divisor;
          
          printf( "\tThis program lists all primes <= n\n\n" );
          printf( "Input n: ");
          scanf( "%d", &n );
          printf( "\n\n\tPrimes <= %d:\n\n", n );

          for ( possible_prime = 2; possible_prime <= n;
                    possible_prime++ ) {
               /* try to find a divisor of possible_prime */
               for ( possible_divisor = 2; 
                    possible_divisor < possible_prime;
                    possible_divisor++ )
                    if ( possible_prime % possible_divisor == 0 )
                         /* found a divisor so possible_prime is not 
                                                             prime */
                         break;
               if ( possible_divisor == possible_prime )
                    /* exhausted possible divisors, so possible_prime 
                        is prime */
                    printf( "%d\n", possible_prime );
          }
     }