C program that will determine if an input year was/will be a leap year.

leapyear.c

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
int main(){
   int year;
   printf("Type a year (up to 4 digits) to determine if it's a leap year:");
   scanf("%d",&year);
   getchar();
   if(((year<0)||(isalpha(year))||(year>9999))){
	    printf("Invalid year. Try again.\n");   
   }else{
	    if((year%4==0)||(year%400==0)){
		    if((year%4==0)&&(year%100==0)){
			    printf("%d is not a leap year\n",year);
			    return 0;
	      }
	      printf("%d is a leap year.\n",year);
	      return 0;
	    }
      printf("%d is not a leap year\n",year);     
   }
return 0;
}