Prime number generator
This program will calculate & list the first n primes, where n is a number specified on the command line or (if none is specified) 100. n is only limited by the size of ints on your platform.
#include <stdio.h> #include <stdlib.h> #include <math.h> int main(int argc, char** argv) { int qty = (argc > 1) ? (int) strtol(argv[1], NULL, 10) : 100; if (qty < 3) qty = 100; unsigned int primes[qty]; primes[0] = 2U; primes[1] = 3U; printf("2\n3\n"); for (int i=2; i<qty; i++) { int j = primes[i-1]; iter: j += 2U; unsigned bound = (unsigned) sqrt((double) j); for (int k=1; k<i; k++) { if (primes[k] > bound) break; /*Not a viable shortcut for small quantities*/ if (!(j % primes[k])) goto iter; } primes[i] = j; printf("%u\n", j); } return 0; }
