#include<string>
#include<cmath>
#include<cstdlib>
#include<iomanip>
#include<iostream>
#include<fstream>
using namespace std;

struct Course
{
    string subject;        //  课程
    double cdt;            //  学分
    double score;          //  成绩
    string quality;        //  成绩性质
    double GPA;            //  绩点      
    Course *next;
    Course(string sub="",double cre=0,double s=0,string Q="");   
    void output();
};
Course::Course(string sub,double cre,double s,string q)   
{
    subject=sub;
    cdt=cre;
    score=s;
    quality=q;
    if(score-50>=1e-5)                                 //将GPA 的计算直接包含在构造函数内，而不是单独拿出去
        GPA=(score-50)*0.1;
    else
        GPA=0.0;
    if(quality=="you") GPA=4.0;
    if(quality=="liang") GPA=3.0;
    if(quality=="zhong") GPA=2.0;
    if(quality=="jige") GPA=1.0;
    if(quality=="bujige") GPA=0.0;
}
void Course::output()
{
    cout<<setw(20)<<subject<<setw(20)<<cdt<<setw(20)<<GPA<<endl;
}


struct Project
{
    Course *head;
    double ave;
    int n;
    Project()
    {
        head=new Course;
        head->next=NULL;
        n=0;
    }
    void add(string sub="",double cre=0,double s=0,string Q="");
    void Add();
    void Sequence();
    void output();
    void aver();
};


void Project::add(string sub,double cre,double s,string q)
{
    Course *array=new Course(sub,cre,s,q);
   
    if(head->next==NULL)
    {
        head->next=array;
        array->next=NULL;
    }
    else
    {
        Course *Q=head->next;
        head->next=array;
        array->next=Q;
    }
    n++;
}


void Project::Add()
{
    string sub;
    double cre;
    char a[20];
    cin>>sub>>cre>>a;
    if(a[0]>='0' && a[0]<='9')
    {
        double s=atoi(a);
        add(sub,cre,s);
    }
    else
    {
        string ss=a;
        add(sub,cre,0,ss);
    }
}
void Project::Sequence()
{
    for(int i=1;i<=n;i++)
    {
        Course *array=head->next,*Q=array->next,*temp=head;  ///temp,array,q  三个指针连续
        int ok=0;
        while(array->next!=NULL)
        {
            if((array->GPA) < (Q->GPA))                    //节点的交换需保存前后两个节点
            {
                temp->next=Q;
                array->next=Q->next;
                Q->next=array;
                temp=Q;
                Q=array->next;
                ok=1;
            }
            else
            {
                temp=temp->next;   ////不用交换，三个指针同时后移
                array=array->next;
                Q=Q->next;
            }
        }
        if(ok==0)
            break;
    }
}

void Project::output()
{
    cout<<setw(20)<<"科目"<<setw(20)<<"学分"<<setw(20)<<"绩点"<<endl;
    Course *array=head->next;
    while(array!=NULL)
    {
        array->output();
        array=array->next;
    }
}
void Project::aver()
{
    Course *array=head->next;
    double sum1=0,sum2=0;
    while(array!=NULL)
    {
        sum1+=array->cdt*array->GPA;
        sum2+=array->cdt;
        array=array->next;
    }
    ave=sum1/sum2;
    cout<<ave<<endl;
    if(ave>1.8)
        cout<<"Congratulations!您的绩点合格,好样的"<<endl;
    else
        cout<<"绩点偏低，努力"<<endl;
}





int main()
{
    Project project;
    int menu,sonmenu=1;
repeat1:
       cout<<"请选择："<<endl;
       cout<<" 0.退出"<<endl;
       cout<<" 1.进入系统   输入分数查阅绩点"<<endl;
       cin>>menu;
       if(menu==0)
           return 0;
       cout<<" "<<setw(50)<<"请按如下顺序输入信息："<<endl;
       cout<<setw(20)<<"科目"<<setw(20)<<"学分"<<setw(20)<<"成绩/等级"<<endl;
       while(sonmenu)
       {
           project.Add();
           cout<<"继续，添加:1"<<endl;
           cout<<"输入结束:0"<<endl;
           cin>>sonmenu;
       }
       //菜单
       cout<<"请选择："<<endl;
       cout<<" A.我要查看 降序排列的 学科总绩点（= 学分 x 绩点）；\n\n B.我要查看 平均绩点。\n"<<endl<<endl;
       cout<<"请选择 (大写)： ";
       char Menu = '0';
       cin>>Menu;
       switch(Menu)
       {
       case 'A':
           project.Sequence();project.output();break;
       case 'B':
           {
               cout<<"您的平均绩点为： ";
               project.aver();
               //    project.OUTAG();
               cout<<endl;break;
           }
       default: cout<<"对不起，您的输入有误！"<<endl<<endl;
       }
       cout<<"继续查询:3"<<endl;
       cin>>Menu;
       if(Menu=='3')
           goto repeat1;
       return 0;
}

出现死循环，注意完善。