Software Testing week fourth--illegal input processing for leap year issues

Judging conditions for leap years:

①, ordinary year can be divisible by 4 and cannot be divisible by 100 for leap years.
A leap year in which ② can be divisible by 400
③, for a large number of years, if the year can be divisible by 3200, and divisible by 172800 is a leap. such as 172,800 years is a leap year, 86,400 years is not a leap

Test Case:

Number	Input	Output
1	2004	This is a leap year
2	2008	This is a leap year
3	2000	This is a leap year
4	1999	Non-leap years for this year
5	1998	Non-leap years for this year
6	-1200	Illegal input

Basic logic:
#include <stdio.h>
void Main ()
{
int year,a;
printf ("Please enter the Year:");
scanf ("%d", &year);

A=1;
else if (year<0)
a=2;

a=0;
if (a==1)
printf ("\n%d This is a leap year \ n";
else if (a==0)
printf ("%d years non-leap year \ n";
Else
printf ("%d input illegal \ n");

　　　　　　
}

Software Testing week fourth--illegal input processing for leap year issues