Yes, of course you can, but before that you need to learn what header files are and how you can use them properly.
file: yourname.h
#ifndef YOUR_NAME_INCLUDE
#define YOUR_NAME_INCLUDE
/* Your function statement here */
#endif
yourname.cpp
#include <iostream.h>
#include "yourname.h"
/* Your function definition here */
main.cpp
#include <iostream.h>
#include "yourname.h"
/* Your function calling here */
To learn more about header files and include statements, click the link below.
Header tutorial