#ifdef name
This directive carries out conditional compilation of the resource file by checking the specified name. If name has been defined using a #define directive, #ifdef directs the Resource Compiler to continue with the statement immediately after #ifdef. If name has not been defined, #ifdef directs the compiler to skip all statements up to the next #endif directive.
The following example demonstrates the correct usage of the #ifdef statement:
#ifdef Debug
errbox BITMAP errbox.bmp
#endif