typedef for function pointer

#include <stdio.h>
typedef  void (*VPF) (int *, int *);
void Square(int *rX, int *rY);
void Swap(int *rX, int *rY);
void PrintVals(VPF,int , int );
 
int main()
{
  int valOne=2, valTwo=5;
  VPF pFunc;

  pFunc = Swap;
  PrintVals ( pFunc, valOne, valTwo);

  pFunc = Square;
  PrintVals ( pFunc, valOne, valTwo);

  return 0;
}
 
void PrintVals( VPF pFunc,int x, int y)
{
  printf("x:%d  y:%d\n",x,y);
  pFunc(&x,&y);
  printf("x:%d  y:%d\n",x,y);
  printf("\n");
}

void Square(int *rX, int *rY)
{
  (*rX) *= (*rX);
  (*rY) *= (*rY);
}

void Swap(int *rX, int *rY)
{
  int temp;
  temp = *rX;
  *rX = *rY;
  *rY = temp;
}

執行結果：

x:2  y:5
x:5  y:2

x:2  y:5
x:4  y:25