Is #define banned in industry standards?

Question

I am a first year computer science student and my professor said #define is banned in the industry standards along with #if, #ifdef, <

Answer 1

If you want your C code to interoperate with C++ code, you will want to declare your externally visible symbols, such as function declarations, in the extern "C" namespace. This is often done using conditional compilation:

#ifdef __cplusplus
extern "C" {
#endif

/* C header file body */

#ifdef __cplusplus
}
#endif