提示的错误有从case 9那里开始case outside of switch in function main;
还有 x  m  is assigned a value which is never used in function main;

#include <stdio.h>

int main()
{
    int yea,mon,day,m,x;

    scanf("%d.%d.%d",&yea,&mon,&day);
    if((yea%4==0&&yea%100!=0)||yea%400==0)
        x=1;
    else
        x=0;
    switch (mon)
    {
        case 1:
        {
            m=day;
            break;
        }
        case 2:
        {
            m=day+31;
            break;
        }
        case 3:
        {
            m=day+31+29;
            break;
        }
        case 4:
        {
            m=day+31+29+31;
            break;
        }
        case 5:
        {
            m=day+31+29+31+30;
            break;
        }
        case 6:
        {
            m=day+31+29+31+30+31;
            break;
        }
        case 7:
        {
            m=day+31+29+31+30+31+30;
            break;
        }
        case 8:
            m=day+31+29+31+30+31+30+31;
            break;
        }
        case 9 :
        {
            m=day+31+29+31+30+31+30+31+31;
            break;
        }
        case 10:
        {
            m=day+31+29+31+30+31+30+31+31+30;
            break;
        }
        case 11:
        {
            m=day+31+29+31+30+31+30+31+31+30+31;
            break;
        }
        case 12:
        {
            m=day+31+29+31+30+31+30+31+31+30+31+30;
            break;
        }
    }
    if(x==1||(x==0&&m<3))
    m=m;
    else
    m=m--;
    printf("%d",m);
    return 0;
}


你的 case 8 少打了一个  {
加上就可以了。
我用 VC6 通过编译

太粗心了。。(*^__^*) 嘻嘻……亏我还累死累活找了半天呢。。。谢谢啦！

细心呀！