Someone explain it... Plz!!!

Question

I'm a bit confused about something in C. I noticed that if I forget to #include <stdio.h>, my code with printf still compiles and runs. I just get a warning.
How does that actually work? I thought it always needed the header file. Why isn't it a hard error, and how does the program figure out where the real printf function is?

https://sololearn.com/compiler-playground/cr6kUJGXqt8x/?ref=app

Answer 1

Ferdous 👾 I believe the compiler is running in C89/C90 compatibility mode by default and the compiler is part of the GNU Compiler Collection (GCC), which historically allowed this as a warning for common cases like printf even in newer modes, though it's discouraged.