习题：switch嵌套

#include<stdio.h>
int main()
{
    int x=1,y=0,a=0,b=0;
    switch(x)
    {
        case 1:
          switch(y)
          {
              case 0: a++;break;
              case 1: b++;break;
           }
        case 2: a++;b++;break;
        case 3: a++;b++;
    }
    printf("a=%d,b=%d\n",a,b);
    return 0;
}