Exercise 4.14 - swap that interchanges two arguments of type t

Question

Define a macro swap(t,x,y) that interchanges two arguments of type t.

/* a macro swap(t,x,y) that interchanges two arguments of type t */

#include<stdio.h>

#define swap(t,x,y) { t _z; \
             _z = x;\
              x = y;\
              y = _z; }

int main(void)
{
    char x,y;
    x='a';
    y='b';
    printf("x= %c \t y= %c\n",x,y);
    swap(char,x,y);
    printf("x=%c \t y=%c\n",x,y);
}


Run this

Explanation

There are two types of macros in C namely object-like and function-like. In object type, we do substitution and in function macros we can send a variable as argument. In this program we are going to use function-like macro to swap.

We do this by defining macro:

#define swap(t,x,y) { t _z; \
                 _z = x;\
                 x = y;\
                 y = _z; }

In the macro, we send type t as an argument and two variables x and y to swap. We create a temperorary variable called _z of type t and use it to swap x and y.

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