2-21.c

c实现的常用几个算法

#include<stdio.h>
void main(void)
{ 
	int year,month,days,flag;
	printf("input year,month:\n");
	scanf("%d%d",&year,&month);
	flag=1;
	switch(month)
	{ 
		case 1:
		case 3:
		case 5:
		case 7:
		case 8:
		case 10:
		case 12:
			days=31;
			break;
		case 4:
		case 6:
		case 9:
		case 11:
			days=30;
			break;
		case 2: 
			if(!(year%4)&&year%100||!(year%400))
				days=29;
			else
				days=28;
			break;
		default:
			flag=0;
	}
	if(!flag)
		printf("error input data\n");
	else
		printf("days=%d\n",days);
}