Два файла .cpp в проекте

#include <iostream>
#include <stdexcept>
#include <locale>
 
using std::cout;
using std::cin;
using std::endl;
 
enum DayOfWeek {MON=1,TUE,WED,THU,FRI,SAT,SUN} ;
 
void printDayOfWeek(DayOfWeek dayOfWeek) {
    switch(dayOfWeek) {
    case 1: cout<<"Monday "<<endl;
        break;
    case 2: cout<<"Tuesday "<<endl;
        break;
    case 3: cout<<"Wednesday "<<endl;
        break;
    case 4: cout<<"Thursday "<<endl;
        break;
    case 5: cout<<"Friday "<<endl;
        break;
    case 6: cout<<"Saturday"<<endl;
        break;
    case 7: cout<<"Sunday "<<endl;
        break;
 
    }
}
 
DayOfWeek readDayOfWeek() {
    int day;
    cin >> day;
    if ( (day<1)||(day>7) ) {
        throw std::range_error("number of day should be in a range [1, 7]");
    }
    return static_cast<DayOfWeek>(day); // cast: int -> DayOfWeek
}

#include <iostream>
#include <locale>
 
using namespace std;
 
enum DayOfWeek {};
void printDayOfWeek();
DayOfWeek readDayOfWeek();
 
int main() {
    std::locale::global(std::locale(""));
    cout<<"Введите день недели 1-7 "<<endl;
    DayOfWeek dow=readDayOfWeek();
    printDayOfWeek(dow);
    system("pause");
    return 0;
}

if ( (day<1)||(day>7) ) {
        throw std::range_error("number of day should be in a range [1, 7]");
    }

#ifndef Day_Of_Week_h
#define Day_Of_Week_h
 
enum DayOfWeek {MON = 1, TUE, WED, THU, FRI, SAT, SUN};
 
void printDayOfWeek(DayOfWeek dayOfWeek);
DayOfWeek readDayOfWeek() ;
 
 
#endif /*Day_Of_W

int main() {
    std::locale::global(std::locale(""));
    cout<<"Введите день недели 1-7 "<<endl;
    DayOfWeek dow;
    try
    {
        dow = readDayOfWeek();
    }
    catch(exception &e)
    {
        cout << e.what() << endl;
        system("pause");
        return 0;
    }
    printDayOfWeek(dow);
    system("pause");
    return 0;
}