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 

You can check out the “previous date problem” program along with its tested test cases here.

First let’s identify the output domain for the previous date problem.

O₁ = Previous date
O₂ = Invalid date

Coming to Input domain,

I₁ = {1 <= date <=31 }
I₂ = {date<0 }
I₃ = {date>31}
I₄ = {1<= month <=12 }
I₅ = {month<1 }
I₆ = {month >31}
I₇ = {2000<= year <=2050}
I₈ = {year<2000 }
I₉ = {year>2050}

In this problem, we can clearly see 2 test cases for output and 9 test cases for input are made.