Macro in different file
//file1.h #define USD 1 //file2.h #define UKP 1 //file3 #include <stdio.h> #include <file1.h> #include <file2.h> #ifdef USD #define currency_rate 46 #endif #ifdef UKP #define currency_rate 100 #endif main() { int rs; rs = 10 * currency_rate; printf ("%d\n", rs); }