Question

How to define undefine and redefine a macro in C

Answer 1

#include <stdio.h>

#define PI 3.14

int main()
{
    printf("PI: %f\n", PI);

    #ifdef PI
    #undef PI
    #endif

    #define PI 3.141592653

    printf("New PI: %f", PI);
    
    return 0;
}




/*
run:

PI: 3.140000
New PI: 3.141593

*/

 

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