c - warning: implicit declaration of function ‘printf’

the warning or error of kind IMPLICIT DECLARATION is that the compiler is expecting a Function Declaration/Prototype..

It might either be a header file or your own function Declaration..

You need to include a declaration of the printf() function.

#include <stdio.h>

You need to include the appropriate header

#include <stdio.h>

If you're not sure which header a standard function is defined in, the function's man page will state this.