c - What is the relationship between #include <stdio.h> and printf()? -

#include <stdio.h> main()  printf(); 

what connection between preprocessor , function?

when c preprocessor reads line #include <stdio.h>, literally reads file stdio.h system directory , replaces line contents. stdio.h contains declarations of printf , other functions, tells c compiler these functions exist in file or library.

when use printf() in code, compiler knows function , knows doesn't have worry it. (if didn't include stdio.h, however, compiler wouldn't have known function looked @ all, have been troublesome , compiler complain this.)

an example stdio.h file printf this:

/* stdio.h */  // declaration of printf int printf(const char *format, ...);  // , bunch of other function declarations...