dev c++ 사용하는데 링크가 안되요.

dev c++ 첨 써보는데 hello world 까지는 잘 컴파일되고 실행 되는데
파일을 여러개로 나눠서 build all 하니까 자꾸 에러가 나네요. 왜그런거죠.
뭔가 설정해줘야 하는게 있나요?

file -> new project -> console application -> ok 해서 project 열고
addtoproject 해서 필요한 파일을 넣고
buildall 을 했는데 컴파일 까지는 되는데 링크가 안 되는거 같아요

밑에 파일 4개 컴파일 하려고 합니다.

// readvar.cpp
// write a stream of persons, using fstream.h 
#include <fstream.h>
#include <strstream.h>
#include <string.h>
#include "writeper.cpp"

istream & operator >> (istream & stream, Person& p)
{ // read fields from stream
	char delim;
	stream.getline(p.LastName, 30,'|');
	if (strlen(p.LastName)==0) return stream; 
	stream.getline(p.FirstName,30,'|');
	stream.getline(p.Address,30,'|');
	stream.getline(p.City, 30,'|');
	stream.getline(p.State,15,'|');
	stream.getline(p.ZipCode,10,'|');
	return stream;
}

int ReadVariablePerson (istream & stream, Person & p)
{ // read a variable sized record from stream and store it in p
  // if read fails, set p.LastName to empty string and return 0
	short length;
	stream . read ((char *)&length, sizeof(length));
	if (stream . fail()){p.LastName[0]=0; return 0;}
	char * buffer = new char[length+1];
	stream . read (buffer, length);
	buffer [length] = 0; // terminate buffer with null
	istrstream strbuff (buffer);
	strbuff >> p;
	return 1;
}
int main(){
	char filename [20];
	Person p;
	cout << "Enter the file name:"<<flush;
	cin.getline(filename, 19);
	ifstream stream (filename, ios::in);
	if (stream.fail()) {
		cout << "File open failed!" <<endl;
		return 0;
	}
	while (1) {
		// read fields of person
		ReadVariablePerson (stream, p);
		if (strlen(p.LastName)==0) break;
		// write person to file
		cout << p;
	}
}

// person.h
#ifndef PERSON
#define PERSON

class Person 
{ public:
	// data members
	char LastName [11]; char FirstName [11]; char Address [16];
	char City [16]; char State [3]; char ZipCode [10];
	// method
	Person (); // default constructor
};

Person::Person ()
{//constructor
	LastName[0]=0; FirstName[0]=0; Address[0]=0;
	City[0]=0; State[0]=0; ZipCode[0]=0;
}

#endif

// writeper.cpp
#include <iostream.h>
#include "person.h"

ostream & operator << (ostream & stream, Person & p)
{ // insert fields into file
	stream<< "Last Name  '" << p.LastName <<"'\n"
		<< "First Name '" << p.FirstName <<"'\n"
		<< "Address    '" << p.Address <<"'\n"
		<< "City       '" << p.City <<"'\n"
		<< "State      '" << p.State <<"'\n"
		<< "Zip Code   '" << p.ZipCode <<"'\n"
		<<flush;
	return stream;
}

// person.cpp
#include <iostream.h>
#include <string.h>
#include "person.h"

istream & operator >> (istream & stream, Person & p)
{ // read fields from input
	cout<<"Enter last name, or <cr> to end: "<<flush;
	stream.getline (p.LastName, 30);
	if (strlen(p.LastName)==0) return stream;
	cout<<"Enter first name: "<<flush; stream.getline(p.FirstName,30);
	cout<<"Enter address: "<<flush; stream.getline(p.Address,30);
	cout<<"Enter city: "<<flush; stream.getline(p.City, 30);
	cout<<"Enter state: "<<flush; stream.getline(p.State,15);
	cout<<"Enter zip code: "<<flush; stream.getline(p.ZipCode,10);
	return stream;
}