CITS-3007-labs/lab01-leap-year/test_leap.c

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>

/* return 0 (false) or 1 (true), depending on whether
 * `year` is a leap year or not.
 */
int is_leap(long year)
{
  return year % 4 == 0            // Every year that is exactly divisible by four is a leap year
         && (year % 100 != 0      // except for years that are exactly divisible by 100
             || year % 400 == 0); // but these centurial years are leap years if they are exactly divisible by 400
}

int main(int argc, char **argv)
{
  argc--;
  argv++;

  if (argc != 1)
  {
    fprintf(stderr, "Error: expected 1 command-line argument (a YEAR), but got %d\n", argc);
    exit(1);
  }

  char *end;

  // clear errno so we can check whether strtol fails
  errno = 0;
  long year = strtol(argv[0], &end, 10);
  int res_errno = errno;

  if (end == argv[0])
  {
    fprintf(stderr, "Error: couldn't interpret '%s' as a number\n", argv[0]);
    exit(1);
  }
  else if (res_errno == ERANGE)
  {
    fprintf(stderr, "Error: '%s' is outside the range of numbers we can handle\n", argv[0]);
    exit(1);
  }
  else
  {
    if (is_leap(year))
    {
      printf("%ld is a leap year\n", year);
    }
    else
    {
      printf("%ld is not a leap year\n", year);
    }
  }
}