#include <iostream.h>
#include <string.h>
#include <stdlib.h>
const char null='\0';

void _() //分隔符
{
    int i;
    for(i=0;i<=79;i++)
        if(i<=79)
            cout<<"-";
}
void menu()
{
    cout<<"\t\t\t\t成绩管理系统"<<endl;
    _();
    cout<<"1.信息录入\t2.信息修改\t3.信息删除\t4.信息排序\t5.退出"<<endl;
    _();
    cout<<"选择:";
}
class student_info
{
protected:
    char *no; //学号
    char *name; //姓名
public:
    void setinfo(char *no1,char *name1); //设置函数
    void printfinfo(); //信息输出
    ~student_info(){delete []no;delete []name;} //析构函数
};
void student_info::setinfo(char *no1,char *name1)
{
    cout<<"输入学号:";
    cin>>no1;
    no1=new char[strlen(no1)+1];
    strcpy(no,no1);
    cout<<"输入姓名:";
    cin>>name1;
    name1=new char[strlen(name1)+1];
    strcpy(name1,name);
}
void student_info::printfinfo()
{
    cout<<"学号:"<<no<<endl<<"姓名:"<<name<<endl;
}
class student_grade:public student_info
{
protected:
    float gokugo;
    float eigo;
    float suugaku;
    float konpyu_ta_;
    static float sum;
    static int count;
    float ave;
public:    
    void setgrade();
    void printfgrade();
};
void student_grade::setgrade()
{
    printfinfo();
    cout<<"输入国语成绩:";
    cin>>gokugo;
    cout<<"输入英语成绩:";
    cin>>eigo;
    cout<<"输入数学成绩:";
    cin>>suugaku;
    cout<<"输入计算机成绩:";
    cin>>konpyu_ta_;
    count++;
}
void student_grade::printfgrade()
{
    cout<<"\n国语成绩:"<<gokugo<<"\n英语成绩:"<<eigo<<"数学成绩:"<<suugaku<<"计算机成绩:"<<konpyu_ta_<<endl;
}
void tj() //添加函数
{
    student_grade g1,*g;
    g=&g1;
    g->setgrade();
}
float student_grade::sum=0;
int student_grade::count=0;
void main()
{
    int select;
    menu();
    cin>>select;
    switch(select)
    {
    case 1:tj();break;
    case 5:system("cls");cout<<"\t\t按任意键退出\n";exit(1);break;
    default:cout<<"错误!"<<endl;
    }
}

输入1

我今天遇到同样的问题 ~!