The ifdef directive makes substitutions based on whether a particular identifier is defined.
#define USA 1
// #define EUP 1
#include
#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