#include<stdio.h>
#include<math.h>
void main()
{
     int x,y;
     double z;
    printf("please input the value of x and y:\n");
    scanf("%d %d",&x,&y);
    if(x>=0&&y>0)
    {
        z=((x*x+1)/(x*x+2))*y;
        printf("z=%.2f\n",z);
    }
    else if(x>0&&y<=0)
    {
        z=(x-2)/(y*y+1);
        printf("z=.2f\n",z);
    }
    else if(x<0)
    {
        z=x+y;
        printf("z=%.2f\n",z);
    }
    else
    {
        printf("sorry!you are wrong!");
    }
}

不管输入多少，输出都是0.。。

(x*x+1) 是int
(x*x+2) 是int
int/int 结果是int

#include<stdio.h>
#include<math.h>
int main()
{
     double x,y,z;
    printf("please input the value of x and y:\n");
    scanf("%lf %lf",&x,&y);
    if(x>=0&&y>0)
    {
        z=((x*x+1)/(x*x+2))*y;
        printf("z=%.2lf\n",z);
    }
    else if(x>0&&y<=0)
    {
        z=(x-2)/(y*y+1);
        printf("z=.2lf\n",z);
    }
    else if(x<0)
    {
        z=x+y;
        printf("z=%.2lf\n",z);
    }
    else 
    {
        printf("sorry!you are wrong!");
    }
}