#include<stdio.h>
#include<math.h>
main()
{
int y,m,t,d,sum=0;
printf("请输入年份:");
scanf("%d",&y);
printf("请输入月份:");
scanf("%d",&m);
printf("请输入天数:");
scanf("%d",&t);
for(int i=1;i<=m-1;i++)
switch(m)
{
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
d=31;
break;
case 4:
case 6:
case 9:
case 11:
d=30;
break;
case 2:
if(y%400==0||y%4==0&&y%100!=0)
d=29;
else
d=28;
break;
}
sum+=d;
}
sum+=t;
printf("%d年%d月%d日是这一年的第%d天",y,m,t,sum);
}
for循环左半拉大括号没写
还有 switch(m) 应该是switch(i)