正在学习类和接口分离与现实

题目是输入成绩，输出并求均值，要求用类和接口分离与现实（书上的作业）

//类的头文件
#ifndef AVERAGEGRADE_GRADELIST_H
#define AVERAGEGRADE_GRADELIST_H

#endif //AVERAGEGRADE_GRADELIST_H
#include <iostream>
class GradeList
{
public:
    explicit GradeList(std::string);
    void setGradeList(std::string);
    std::string getGradeList() const;
    void DisplayMessage() const;
    static void range();
private:
    std::string coursename;

};

//函数关联.h的.cpp文件
#include "GradeList.h"
#include <iostream>
#include<string>

using namespace std;
GradeList::GradeList(string name)
{
    setGradeList(name);
}

void GradeList::setGradeList(string name)
{
    if(name.size()<=25) coursename=name;
    else
    {
        coursename=name.substr(0,25);
        cerr<<"Name\""<<name<<"\"exceeds maxium length"<<endl;
    }
}

string GradeList::getGradeList()const
{
    return coursename;
}

void GradeList::DisplayMessage()const
{
    cout<<"Welcome to the grade list for\n"<<getGradeList()<<"!\n"<<endl;
}

void GradeList::range()
{
    int total=0;
    int i=1,n;
    cout<<"Hw many students in your class?";
    cin>>n;
    while(i<=n)
    {
        cout<<"Enter grade:";
        int grade ;
        cin>>grade;
        total+=grade;
        i++;
    }
    float average =total/10;
    cout<<"\ntotal of all grades is"<<total<<endl;
    cout<<"Class average is"<<average<<endl;
}

//main函数
#include "GradeList.h"
int main()
{
    GradeList myGradeList("C++");
    myGradeList.DisplayMessage() ;
    myGradeList.range();
    return 0;
}

但是最后报错 collect2.exe: error: ld returned 1 exit status ninja: build stopped: subcommand failed. 不知道问题在哪，求大佬解答