Code

 Header...
void unwise_function (double *pp,double *qq);

 int main(){
   ... 

»  double x=17.1, y, *p, *q;// p, q are pointers

»  p=&x;// The value of p is now the address of x.
// If we do anything with or to *p it's doing it to x:

»  printf(" p: %p\n", p);
»  printf(" *p: %g\n", *p);

»  y=*p;// Exactly the same as y = x;
»  *p=3.14159;// Exactly the same as x = 3.14159;
 
  // Now let's make p point to y: 
»  p=&y;
»  *p=1.414;
»  q=&x;// The value of q is now the address of x 

»  unwise_function(p, q);// The same as unwise function(&y, &x);

  // Now x has the value 73.2, y has the value 2.5 
»  printf("x: %f y: %f\n", x, y);
}

 void unwise_function(double *p2,double *q2){
   ... 

»  *p2=2.5;
»  *q2=73.2;
}