C program to Find Previous Date

The program prints previous date of the entered input. It validates leap year, month and date to check whether the given date is valid or not. We have simply used nested if in the logic to achieve the functionality.

C Program to determine the previous date

Program:

#include<conio.h>
#include<stdio.h>

int
main ()
{
  int month, date, year, valid = -1, leap_year = -1, invalid_input = -1;
  printf ("please enter a date = ");
  scanf ("%d", &date);
  printf ("please enter a month = ");
  scanf ("%d", &month);
  printf ("please enter a year = ");
  scanf ("%d", &year);
  if ((date > 0 && date <= 31) && (month >= 1 && month <= 12)
      && (year >= 2000 && year <= 2050))
    {
      invalid_input = 1;
      // finding given input is a leap year or not
      if ((year % 4) == 0)
  {
    leap_year = 1;
    if ((year % 100) == 0)
      {
        if ((year % 400) == 0)
    {
      leap_year = 1;
    }
        else
    {
      leap_year = -1;
    }
      }
  }
      if (month == 2 && leap_year == 1 && date > 29)
  valid = -1;
      else if (month == 2 && leap_year == -1 && date > 28)
  valid = -1;
      else
  valid = 1;
    }

  if ((month == 6 || month == 4 || month == 9 || month == 11) && date > 30)
    valid = -1;

// validating & finding output


  if (valid == 1)
    {
      printf ("Entered date = %d-%d-%d", date, month, year);

      if (date == 1)
  {
    if (month == 1)
      {
        date = 31;
        month = 12;
        year--;
      }
    else if (leap_year = 1 && month == 3)
      {
        date = 29;
        month--;
      }
    else if (leap_year == -1 && month == 3)
      {
        date = 28;
        month--;
      }
    else if (month == 2 || month == 4 || month == 6 || month == 8
       || month == 9 || month == 11)
      {
        date = 31;
        month--;
      }
    else
      {
        date = 30;
        month--;
      }
  }
      else
  {

    date--;
  }
      printf ("\nPrevious date = %d-%d-%d \n", date, month, year);
    }

  if (valid == -1 && invalid_input == 1)
    printf ("\n Not a valid date");

  if (invalid_input == -1)
    printf ("\n Invalid Input");

  return 0;
}

Output:

Testing the program:

Invalid Date:

please enter a date = 31
please enter a month = 6
please enter a year = 2030

 Not a valid date

Previous Date:

please enter a date = 21
please enter a month = 6
please enter a year = 2030
Entered date = 21-6-2030
Previous date = 20-6-2030