importance of enclosing macro expansion wihtin parentheses

 importance of enclosing macro expansion wihtin parentheses

/* Program to illustrate the importance of enclosing macro expansion wihtin parentheses */

If we fail to enclose the entire macro expansion in the parentheses then we may get some unexpected results.

Consider the following program:

#include<stdio.h>

#define SQUARE(x) x*x //Macro definition without parentheses

int main()

{

int i;

i=27/SQUARE(3);

printf("%d",i);

return 0;

}

Here we expected that the output would be 3.

Lets see the actual output:

Shocked, the reason is that the above macro is expanded as:

i=27/3*3;

Following the associativity rule (left to right) first 27/3 is solved which gives 9.

i.e. i=9*3;

So we get the out put as 27 not 3.

So how to write the macro for getting the correct out put.

Following program will illustrate you this thing.

#include<stdio.h>

#define SQUARE(x) (x*x) //Macro definition with parentheses

int main()

{

int i;

i=27/SQUARE(3);

printf("%d",i);

return 0;

}

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