CODEWITHSUNDEEP
cmacrosc-preprocessor
Suraj
Suraj

Reputation: 91

How is value of macro getting change

#include <stdio.h>
int main()
{
    int var;
    printf("write the value of var:\n");
    scanf("%d", &var);
#define NUM var

    printf("The value of S is %d\n", NUM);
    var = var + 1; //changing the value of variable 'var'
    printf("New value of S is %d", NUM);
return 0;
}

Following is the result...

write the value of var:
10
The value of S is 10
New value of S is 11
[Program finished]

In this program, I want to make constant the value of variable 'var' once it's entered by user. so, I have defined a macro with macro templet 'NUM' and macro expansion 'var'. But when I change the value of 'var' on execution time then the value of 'NUM' also get changed. Don't know how? Actually I don't know that can we use any variable in macro expansion ?

Upvotes: 0

Views: 275

Answers (1)

0___________
0___________

Reputation: 67741

Preprocessing is done before the actual C code compilation. It simply textually replaces the token NUM with token var.

So after the preprocessing your function is:

int main()
{
    int var;
    printf("write the value of var:\n");
    scanf("%d", &var);

    printf("The value of S is %d\n", var);
    var = var + 1; //changing the value of variable 'var'
    printf("New value of S is %d", var);
return 0;
}

This main function is being compiled. As you see the NUM has been replaced with var and the result is obvious.

Upvotes: 2

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