C++ 接口和实现分离实现错误

Question

上课的时候老师提到了个这个东西，然后给了代码实例，可是无论如何执行main.cpp都会有些错误Example DATE class – Using METHOD Three File 1 - Date.h   Header file #pragma once        // needed to work class Date { public:     void get();      // function header for inputting the date     void write();    // function header for outputting the date private:     int month;       // month (between 1 and 12)     int day;         // day (between 1 and 31)     int year;        // year (between 0 and 99) }      File 2 – Date.cpp  Implementation file #include <iostream> #include <iomanip> using namespace std; #include "Date.h"  // Include the library/file name of the class in quotes  void Date::get() {     char slash;    // Allows for inputting in the format MM/DD/YY     cin >> month >> slash >> day >> slash >> year; }  void Date::write() {     cout << "The date you entered was: " << setw(2) << month << "/" << setw(2) << day << "/" << setw(2) << year << endl; }   File 3 – Driver/Test fileImp.Date.cpp  #include <iostream> #include <iomanip> using namespace std; #include "Date.h"      // include DATE class header file name  int main () {     Date aDate;        // declaring A as a type Date      cout << "Enter a date in the form MM/DD/YY:  \n";     aDate.get();       // Function which will input our date     aDate.write();     // Function which will output our date     return 0;