现在编译没有错误老是链接有错误
大家能不能详细解释一下
我是没有编程基础才学几天的新手
谢谢
//编写一个用于院校人事管理的程序，要求能够输入、显示各类人员的信息。
//假设院校有四类人员：学生，教师，员工和在职进修教师，他们都有姓名，性别、电话等共同信息
//学生具有年级、专业课程和各科成绩的信息，员工具有所在部门、工资的信息
//教师具有所在部门、工资和所授课程的信息，在职进修教师兼有教师和学生两类信息
#include<iostream>
#include<string>
using namespace std;
class College_person{
protected:
    string name;
    string sex;
    int phone;
    string duty;
public:
    College_person(string tempduty="学生"):duty(tempduty)
    {
        cout<<duty<<endl;
        cout<<"姓名：";
        cin>>name;
        cout<<"性别：";
        cin>>sex;
        cout<<"电话：";
        cin>>phone;
    }
    void display()
    {
        cout<<"职务："<<duty<<"  姓名："<<name<<"  性别："<<sex<<"  电话："<<phone<<endl;
    }
};
class Student:public College_person{
protected:
    int grade;
    string study_class[3];
    int score[3];
    int i;
public:
    Student():College_person("学生")
    {
        cout<<"年级：";
        cin>>grade;
        cout<<"专业课程：";
        for(i=0;i<3;i++)
        cin>>study_class[i];
        cout<<"各科成绩：";
        for(i=0;i<3;i++)
        cin>>score[i];
    }
    void show()
    {
        College_person::display();
        cout<<"年级："<<grade<<"  专业课程：";
        for(i=0;i<3;i++)
        cout<<study_class[i]<<"  ";
        cout<<"  各科成绩：  ";
        for(i=0;i<3;i++)
        cout<<score[i]<<"  ";
        cout<<endl;
    }
};
class Workers:virtual public College_person{
protected:
    string department;
    float salary;
public:
    Workers():College_person("员工")
    {
        cout<<"部门：";
        cin>>department;
        cout<<"工资：";
        cin>>salary;
    }
    void show()
    {
        College_person::display();
        cout<<"部门："<<department<<"  工资："<<salary;
        cout<<endl;
    }
};
class Teachers:public Workers{
protected:
    int i;
    string teach_class[3];
public:
    Teachers():Workers(),College_person("教师")
    {
        cout<<"所授课程：";
        for(i=0;i<3;i++)
        cin>>teach_class[i];
    }
    void show()
    {
        Workers::show();
        cout<<"  所授课程：";
        for(i=0;i<3;i++)
        cout<<teach_class[i]<<"  ";
        cout<<endl;
    }
};
class Advanced_teacher:public Student,public Teachers{
public:
    int i;
    Advanced_teacher():Student(),Teachers(),College_person("在职进修教师")
    {}
    void show()
    {
        Student::show();
        Teachers::show();
    }
};
void main()
{
    Student a;
    a.show();
    Workers b;
    b.show();
    Teachers c;
    c.show();
    Advanced_teacher d;
    d.show();
}