#include /* We need the Input & Output streams */ #include /* We need the mathematical square root for the test */ using namespace std; /* We use Standard notation. */ /************************************************************************** * * * This litle Demo Program, finds all the Prime Numbers, up to a Maximum. * * * **************************************************************************/ int main() /* The main program function */ { int i, j, noprim; /* Some iterators */ int max = 5000; /* On other systems, the Max integer to be tested, could be higher */ cout << "Prime Numbers less than " << max << endl << "2"; /* 2 is the first Prime Number! */ for (i = 3; i < max; i++) /* Loop trough all the numbers to be tested */ { noprim = 0; /* For each tested number, the flag is initialised */ if (i == 4) /* The integer 4 can cause some troubles, so we skip it */ { noprim = 1; /* 4 is not a Prime Number */ continue; /* On to the next iteration... */ } for (j = 2; j <=sqrt(i); j++) /* This is the test loop itself */ { if (i % j == 0) /* There is no modulo - A divaider - Not a Prime number */ { noprim = 1; /* The flag of A Composite Number is up! */ break; /* We can skip to the next number to test*/ } } if (noprim == 0) /* After the test, the flag is still down. We found a Prime Number! */ { cout << ", " << i; /* Output the new Prime Number */ } } return 0; /* Done! */ }

Prime Numbers.cpp