Leap year program

 #include <stdio.h>

int main()
{
  int year;

  printf("Enter a year to check if it is a leap year\n");
  scanf("%d", &year);

  if (year%400 == 0) // Exactly divisible by 400 e.g. 1600, 2000
    printf("%d is a leap year.\n", year);
  else if (year%100 == 0) // Exactly divisible by 100 and not by 400 e.g. 1900, 2100
    printf("%d isn't a leap year.\n", year);
  else if (year%4 == 0) // Exactly divisible by 4 and neither by 100 nor 400 e.g. 2020
    printf("%d is a leap year.\n", year);
  else // Not divisible by 4 or 100 or 400 e.g. 2017, 2018, 2019
    printf("%d isn't a leap year.\n", year); 
 
  return 0;
}

Output of program: