main.cpp
------------------------------
#include <cstdlib>
#include "out.h"

int main()
{
    string s1;
    cin>>s1;
    out(s1);
    system("PAUSE");
    return EXIT_SUCCESS;
}
out.cpp
----------------------------
#include "out.h"

void out(string s1){
    cout<<"hello,";
    for(int i=0;i<s1.size();i++)
        cout<<s1[i];
    cout<<endl;
}

out.h        
---------------------------------
#include <iostream>
#include <string>
using namespace std;

void out(string s1);