void main()
{
int x,y,flag;
printf("請輸入x:");
scanf("%d",&x);
flag=x<0?-1:(x<10?1:2);
switch(flag)
case -1:y=x;break;
case 1:y=2*x-1;break;
case 2:y=3*x-1;
}
printf("y=%d\n",y);