Scope of macros

While this is written in K & R "The scope of a name defined with #define is from its point of definition to the end of the source file being compiled."

Why this piece of code is working fine ?

Code:

#include <stdio.h>

#define MAX MAXX
#define MAXX 10

int main() {
    printf("%d", fun());
    return 0;
}


int fun() {
    return MAX;
}

and why this code is showing error ?

Code:

#include <stdio.h>

#define MAXX 10
#define MAX MAXX
#undef MAXX


int main() {
    printf("%d", fun());
    return 0;
}


int fun() {
    return MAX;
}

> and why this code is showing error ?
Because line 4 isn't transformed into
#define MAX 10

Originally Posted by _arjun

"The scope of a name defined with #define is from its point of definition to the end of the source file being compiled."

If you use #undef SYMBOL then you are ending the scope of SYMBOL

Originally Posted by _arjun

and why this code is showing error ?

Code:

#include <stdio.h>

#define MAXX 10
#define MAX MAXX
#undef MAXX

int fun() {
    return MAX;
}

int main() {
    printf("%d", fun());
    return 0;
}

The replacements only affect the code lines, not the preprocessor lines. Try the following instead:

Code:

#include <stdio.h>

#define MAXX 10
const int MAX=MAXX;
#undef MAXX

int fun() {
    return MAX;
}
 
int main() {
    printf("%d", fun());
    return 0;
}