求某年/月/日是星期几

/*求某年/月/日是星期几*/
#include<stdio.h>
//星期函数声明 
int weekday(int year,int month,int day); 
void main()
{
	int year,month,day,flag;
	int days[12]={31,28,31,30,31,30,31,31,30,31,30,31};
	printf("请输入年份：\n");
	scanf("%d",&year); 
	printf("请输入月份：\n");
	scanf("%d",&month); 
	printf("请输入日号：\n");
	scanf("%d",&day);
	days[1] = (year%4==0 && year%100!=0 || year%400==0) ? 29:28;//闰年调整
	if(year>0 && month>0 && month<13 && day>0 && day<=days[month-1])//判断输入是否正确
	{
		flag=weekday(year,month,day);
		switch(flag)
		{
			case 0:
				printf("%d年%d月%d日是星期日\n",year,month,day);
				break;
			case 1:
				printf("%d年%d月%d日是星期一\n",year,month,day);
				break;
			case 2:
				printf("%d年%d月%d日是星期二\n",year,month,day);
				break;
			case 3:
				printf("%d年%d月%d日是星期三\n",year,month,day);
				break;
			case 4:
				printf("%d年%d月%d日是星期四\n",year,month,day);
				break;
			case 5:
				printf("%d年%d月%d日是星期五\n",year,month,day);
				break;
			case 6:
				printf("%d年%d月%d日是星期六\n",year,month,day);
				break;
			default:
				printf("输入错误，请重新输入！\n",year,month,day);
		}	
	}else
	{
		printf("输入错误，请重新输入！\n");	
	}
} 
int weekday(int year,int month,int day)
{
	int Weekday=(day+2*month+3*(month+1)/5+year+year/4-year/100+year/400)%7;
	return Weekday;
}

运行结果：