Generic C / Python Polyglot (#184)

A polyglot — coming from the Greek words πολύς (many) and γλώττα (tongue) — is a piece of source code which can run in multiple languages, often performing lan­guage-dependent tasks.
Even though such a source code’s feature may not seem particularily useful or possible with certain lan­guage combinations, trying to bend not one but multiple lan­guage’s syntactic rules and overall behavior is still interesting.

An example of a rather simple polyglot would be a Python 2 / Python 3 polyglot — if one counts those as two separate languages. Because of their enormous similarities, one can pick out differences and use those to determine which lan­guage runs the source code.

if 1/2>0:print("Python 3")
else:print("Python 2")

Utilizing Python’s version difference re­gard­ing integer division and real division is one of the most common ways to tell them apart, as it can also be used to only control a specific part of a program instead of having to write two nearly identical programs (increases the program’s style and cuts on bytes — an important consideration if one golfs a polyglot).

However, polyglots combining languages that are not as similar as Python 2 and Python 3 require more effort. The following is a gen­er­al Python 2 / C polyglot, meaning that nearly all C and Python 2 programs can be mixed using this template (there are a few rules both languages need to abide which will come apparent later).

#define _\
"""
main(){printf("C");}
#define _"""
#define/*
print"Python 2"
#*/_f

In the above code, main(){printf("C");} can be nearly any C code and print"Python 2" can be nearly any Python 2 code.
Language determination is exclusively done via syntax. A C compiler⁠¹ sees a #define statement and a line continuation \, another two #define statements with a block comment in between and actual compilable C source code (view first emphasis).Python, on the other hand, treats all octothorps, #, as comments, ignoring the line continuation, and triple-quoted strings, """...""", as strings rather than statements and thus only sees the Python code (view second emphasis).

My first ever polyglot used this exact syntactical lan­guage differentiation and solved a task titled Life and Death of Trees (link to my answer).