哈喽C!输入某年某月，计算这个月的天数

#include<stdio.h>
main()
{	int month,years;
	printf("请输入年月：");
	scanf("%d",&years),scanf("%d",&month);
	//for(i=1;i<=12;i++)为什么错了 
	if(years%400==0)
		printf("the month is 29 days");
	else if(month==2)//必须加这个条件限制 
	printf("the month is 28 days");
			switch(month)
			{case 1:printf("the month is 31 days");break;
		//	case 2:printf("the month is 28 days");break;
			case 3:printf("the month is 31 days");break;
			case 4:printf("the month is 30 days");break;
			case 5:printf("the month is 31 days");break;
			case 6:printf("the month is 30 days");break;
			case 7:printf("the month is 31 days");break;
			case 8:printf("the month is 31 days");break;
			case 9:printf("the month is 30 days");break;
			case 10:printf("the month is 31 days");break;
			case 11:printf("the month is 30 days");break;
			case 12:printf("the month is 31 days");break;
			}	
 }