Check whether a date is valid or not Program in C

/*Program to check whether a date is valid or not*/
#include<stdio.h>
int main(void)
{
	int d,m,y;
	int flag=1,isleap=0;

	printf("Enter date(dd/mm/yyyy): ");
	scanf("%d/%d/%d",&d,&m,&y);
	if(y%100!=0 && y%4==0  ||  y%400==0)
		isleap=1;

	if(y<1850 || y>2050 || m<1 || m>12 || d<1 || d>31)
		flag=0;
	else if(m==2)	/*Check for number of days in February*/
	{
		if(d==30 || d==31 || (d==29 && !isleap) )
			flag=0;
	}	
	else if(m==4 || m==6 || m==9 || m==11)/*Check days in April,June,Sept,Nov*/
	{	
		if(d==31)
			flag=0;
	}
	
	if(flag==0)
		printf("Not a valid date\n");
	else
		printf("Valid Date \n");
	return 0;
}/*End of main()*/