//ppp.c  --- test pointer of pointer of int (int**)
#include <stdio.h>
int x=38, y = 49;
void haha(int**, int**);
int main( ) {
   int* pa = &x;  // pa points to x
   int *pb = &y;
   printf("*pa=%d, *pb=%d\n", *pa, *pb);
   printf(" x=%d, y=%d\n", x, y);
   printf("calling haha..\n");
   haha(&pa, &pb);   // Note !
   printf("*pa=%d, *pb=%d\n", *pa, *pb);
   printf(" x=%d, y=%d\n", x, y);
   printf(" 注意 x 與 y 並沒有改變!\n");
   return 0;
}
void haha(int** p, int** q) {
  int* t;   // t is a pointer to int; *t is an int
  t = *p; *p = *q; *q = t;
}
/***
6:38am ccbsd2:pointers/> gcc ppp.c
6:38am ccbsd2:pointers/> ./a.out
*pa=38, *pb=49
 x=38, y=49
calling haha..
*pa=49, *pb=38
 x=38, y=49
 注意 x 與 y 並沒有改變!
6:38am ccbsd2:pointers/>
***/