undef : undef « Preprocessor « C Tutorial

1. C Tutorial
2. Preprocessor
3. undef

To undefine the value defined by '#define' and specify a new value.

#include <stdio.h>

#define VAL 40;     
#undef  VAL          
#define VAL 50      

main()
{
    printf ("%d\n", VAL);  
}

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