如题。我想在宏定义中实现两值互换，而不是用函数，怎么做到？

1. #import <Foundation/Foundation.h>
   
2. #define Exchange(a, b) a = b - a;b = b - a;a = b + a;
   
3. 
   
4. int main(int argc, const char * argv[])
   
5. {
   
6.     int a = 5;
   
7.     int b = 7;
   
8.    
   
9.     Exchange(a, b);
   
10.    
    
11.     NSLog(@"a = %d, b = %d", a, b);
    
12.    
    
13.     return 0;
    
14.    
    
15. }

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1. #define swap(x,y)  {x= x+y; y=x-y; x=x-y;}

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