C Tutorial/Preprocessor/ifndef
ifndef
#ifndef is used to check whether a particular symbol is defined.
#define USA 1
//#define EUP 1
#include <stdio.h>
#ifndef USA
#define currency_rate 100
#endif
#ifndef EUP
#define currency_rate 46
#endif
main()
{
int rs;
rs = 10 * currency_rate;
printf ("%d\n", rs);
}460
