输入年和月，输出该月有几天。
c++

#include <bits/stdc++.h>
using namespace std;
int main()
{
	int y,m;
	cin>>y>>m;
	switch(m){
		case 1:
		case 3:
		case 5:
		case 7:
		case 8:
		case 10:
		case 12:
			printf("%d",31);break;
		case 2:
			if(y%4==0&&y%100!=0||y%400==0){
				printf("%d",29);break;
			}else{
				printf("%d",28);break;
			}
		case 4:
		case 6:
		case 9:
		case 11:
			printf("%d",30);break;
	}
	return 0;
}