Usage: "prime N" prints prime number higher or equal to N

prime.cpp

#include <stdio.h>
#include <math.h>
#include <algorithm>

int main (int argc, char **argv)
{
  if(argc!=2)  {printf("Usage: prime N\n  Prints prime number higher or equal to N\n"); return 0;}
  unsigned long long N, N0;
  sscanf (argv[1], "%llu", &N);  N0=N;
  unsigned m = std::min((unsigned long long)(sqrt(N))+10, N);
  for (;;)
  {
    for (unsigned i=3; i < m; i+=2)
      if (N%2==0 || N%i==0)
        {if (N%2==0)  i=2;  printf("%llu / %u%s", N, i, (i>1000 || N==N0)? "\n" : "\r"); goto next;}
   printf("%llu is prime!!!\n", N); break;
next:
    N++;
  }

  return 0;
}