ifdef : ifdef « Preprocessor « C Tutorial

1. C Tutorial
2. Preprocessor
3. ifdef

The ifdef directive makes substitutions based on whether a particular identifier is defined.

#define USA 1
// #define EUP 1

#include <stdio.h>
#ifdef USA
#define currency_rate 46
#endif

#ifdef EUP
#define currency_rate 100
#endif
main()
{
    int rs;
    rs = 10 * currency_rate;
    printf ("%d\n", rs);
}

460