What is the significance of forward declaration in C programming?

Question

I am now learning C programming through Learn C the Hard Way by Zed A. Shaw. There is this code (taking from his website):

#include 
#include          


        

Answer 1

You should declare functions in the order that makes sense. This should be described in the coding style document you follow. One example of common design is:

• h-file with all publically available function declarations.
• c-file with all private function declarations at the top.
• then in the same c-file follows the function definition of the public functions.
• and then at the end of that c-file, the function definition of the private functions.

In addition to style and design concerns, ancient versions of C would start to "make up" function parameters and return types if there was no prototype at all visible before the function call.