计算函数F(x,y,z)=(x+y)/(x-y)+(z+y)/(z-y)的值

 #include <iostream.h>
float fun(float,float);
void main()
{
 float x,y,z,  sum=0   ;
 cout<<"input x,y,z:";
 cin>>x>>y>>z;
 sum=fun(x,y)/fun(x,-y)+fun(z,y)/fun(z,-y) ;
 cout<<"sum="<<sum<<endl;
}
float fun(float a,float b)
{
 float value;
 value=a+b;
 return    value    ;
}