// this file illustrates macro definitions and compares them to
// parameter passing in functions, both by value and by reference.

#include <iostream.h>

#define TRUE 1                    // TRUE is not a variable!!
#define FALSE 0
#ifndef PI 
 #define PI 3.1415927
#endif
#ifndef NULL
 #define NULL 0
#endif

#define PSWAP(type,x,y) { type temp; \
		          temp = x; x = y; y = temp; }


void fswap(int x, int y)
{ int temp;
  temp = x; x = y; y = temp; 
}

void rswap(int *x, int *y);     // function to be defined later

void main()
{ int a, b;
  double u, v;
  a = 4;
  b = 5;
  u = PI;   v = PI*PI;
  


//  PSWAP(int,a,b)            // can't call functions like this!

// #undef PSWAP   // PSWAP can't be used after this point

// PSWAP(double,u,v)

//  cout << "\na: " << a << ",  b: " << b;
//  cout << "\nu: " << u << ",  v: " << v;

  rswap(&a,&b);            

  cout << "\nafter rswap:  a: " << a << ",  b: " << b;

  cout << "\n";
}

// can't put macro definitions here.  Why?


// functions are fine though, as long as they were declared earlier

void rswap(int* x, int* y)
{ int temp;            
  temp = *x;            
  *x = *y;         // what if I did x = y?
  *y = temp;
}