C/C++ :: How To Add Functions To Class In A Separate File

I could do the assignment if all i had to do was create a function within one file, call it in the main class, and that would be done with it. no, my teacher wants us to have our main program, a header and a separate class file and create functions in it in which we can then use in the main file.

This is the main file:

#include <iostream>
#include "call.h"
using namespace std;
int main() {
int length; //holds the length of the call in minutes
int hour; //holds the hour od the day(0-23 military time)

[Code] .....