哪位好人可以帮我看看错哪了

Description
输入年和月，判断该月有几天？

Input
输入年和月，格式为年\月。

Output
输出该月的天数。
#include <stdio.h>
#include <stdlib.h>
int main()
{
int y,m;
scanf("%d\%d",&y,&m);
if(y%400==0||(y%100!=0&&y%4==0))
{
switch(m)
{
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:printf("31");break;
case 2:printf("28");break;
case 4:
case 6:
case 9:
case 11:printf("30");break;
}
}
else
{
switch(m)
{
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:printf("31");break;
case 2:printf("29");break;
case 4:
case 6:
case 9:
case 11:printf("30");break;
}
}
return 0;
}

输出格式不知道题目有没有要求，就按题主写的格式。修改如下，供参考：

#include <stdio.h>
#include <stdlib.h>
int main()
{
   int y,m,flg = 0;
   scanf("%d\\%d",&y,&m);// \是转义符
   if((y%4==0 && y%100!=0) || (y%400==0))
      flg = 1;               //修改
   switch(m){
          case 1:
          case 3:
          case 5:
          case 7:
          case 8:
          case 10:
          case 12:printf("31");break;
          case 2:
                 if(flg) printf("29");//修改
                 else    printf("28");
                 break;
          case 4:
          case 6:
          case 9:
          case 11:printf("30");break;
   }
//else
//{
//switch(m)
//{
//case 1:
//case 3:
//case 5:
//case 7:
//case 8:
//case 10:
//case 12:printf("31");break;
//case 2:printf("29");break;
//case 4:
//case 6:
//case 9:
//case 11:printf("30");break;
//}
//}
    
     return 0;
}

你可以先说说问题所在