Implicit function declarations in C

Question

What is meant by the term \"implicit declaration of a function\"? A call to a standard library function without including the appropriate header file produces a warning as i

Answer 1

Because of historical reasons going back to the very first version of C, functions are assumed to have an implicit definition of int function(int arg1, int arg2, int arg3, etc).

Edit: no, I was wrong about int for the arguments. Instead it passes whatever type the argument is. So it could be an int or a double or a char*. Without a prototype the compiler will pass whatever size the argument is and the function being called had better use the correct argument type to receive it.

For more details look up K&R C.