gistfile1.c

#include <stdlib.h>

int main()
{
   int done = 0;
   char * de = (char *)"  ";
   while(!done)
   {
      int d;
      done = 1;

      if(*de == ':')
         de++;

      while((d = (int)strtoul(de, &de, 10) && d <= 31))
      {
         done = 1;
      }
   }
   return 0;
}