Question

所以基本上我的教授给了我们班级学生，并告诉我们实现所有功能并为函数编写一个main。我正在努力做到这一点，但我无法弄清楚出现的错误，在我的所有访问器函数中它告诉我nCredits，gpa和s都没有在范围内声明。我认为这与第二个构造函数有关，但我不确定究竟是什么问题。第二个构造函数和displayStRec函数也提供给了我们的类，我只是不知道如何使用成员函数中的变量重新命名这个程序。

#include <iostream>
using namespace std;
class student
{
            public:
                            student();
                            student(string s, double gpa, int nCredits);
                            ~student(); //destructor
                            void changeCredits(int nCredits);

                            int getCredits();

                            void changeGPA(double gpa);

                            double getGPA();

                            void displayStRec();

            private:
                            string name;
                            double GPA;
                            int credits;
};

student::student()
{
            name = "No name yet";
            GPA = 0;
            credits = 0.0;
            cout << "Default constructor entered!" << endl;
}
student::student(string s, double gpa, int nCredits)
{
            name = s;
            GPA = gpa;
            credits = nCredits;
            cout << "Second constructor entered!" << endl;
}

void student::changeCredits(int nCredits){
 cout << "Enter credits earned:" << endl;
 cin >> nCredits;
}

int student::getCredits(){
return nCredits;
}

void student::changeGPA(double gpa){
 cout << "Enter GPA: " << endl;
 cin >> gpa;
}

double student::getGPA(){
 return gpa;
}

void student::displayStRec()
{
        cout << "   Name: " << s <<endl;
        cout << "    GPA: " << gpa <<endl;
        cout << "Credits: " << nCredits <<endl;
}

student::~student()
{
            cout << "Destructor entered!" << endl;
}

int main()
{
            student s1,s2("John",4.0,42);
            s2.changeCredits(nCredits);
            s2.getCredits();
            s2.changeGPA(gpa);
            s2.getGPA();
            s2.displayStRec();
            return 0;
}

Answer 1

您已经使用了三个未声明的变量。我会一个接一个地打他们。

缺少s

void student::displayStRec()
{
        cout << "   Name: " << s <<endl;
        cout << "    GPA: " << gpa <<endl;   
        cout << "Credits: " << nCredits <<endl;  
}

在此函数中，您尝试输出一些未在displayStRec范围内声明的变量s。您在构造函数中使用s来初始化名称，将其复制到成员变量name。那么，s现在已经消失了！但是name在对象的生命周期中仍然存在。所以，只需使用name。

void student::displayStRec()
{
        cout << "   Name: " << name <<endl;  //Change it here
        cout << "    GPA: " << gpa <<endl;
        cout << "Credits: " << nCredits <<endl;
}

缺少nCredits和gpa

在您的主要功能中，您使用了两个未声明的变量。

int main()
{
            student s1,s2("John",4.0,42);
            s2.changeCredits(nCredits);  //What nCredits?
            s2.getCredits();
            s2.changeGPA(gpa);           //What gpa?
            s2.getGPA();
            s2.displayStRec();
            return 0;
}

这导致了一个问题......你想要将他们的学分改为到？你想改变他们的gpa 到是什么？换句话说，你的程序不应该有输入参数吗？也许在你的任务的某个地方，你的教授告诉你要提供什么价值。您将需要某种常量，或者您需要从cin收集用户输入。

哦，顺便说一句，这是毫无意义的

void student::changeGPA(double gpa){
    cout << "Enter GPA: " << endl;
    cin >> gpa;
}

此函数将接受用户输入并更新变量gpa，该变量在本地范围内声明并立即丢弃。不太有用。

此外，它接受输入值（double gpa），但也收集来自cin的输入。两个为什么两个？无法同时将其更新为两个值！

我的猜测是应该更新对象的GPA，这是在成员范围内声明的。像这样：

void student::changeGPA(){
    cout << "Enter GPA: " << endl;
    cin >> GPA;
}

或

void student::changeGPA(double gpa){
    GPA = gpa;
}

结论

以下其中一项必须如此：

您错误地复制了代码示例
教授给了你一个技巧问题
教授有点无能为力或者有点过度劳累

Answer 2

我已经完成并删除了我教授试图对我们施加压力的第二个构造函数，这个程序现在运行正常：

#include <iostream>
using namespace std;
class student
{
            public:
                            student();
                            student(string s, double gpa, int nCredits);
                            ~student(); //destructor
                            void changeCredits();

                            int getCredits();

                            void changeGPA();

                            double getGPA();

                            void displayStRec();

            private:
                            string name;
                            double GPA;
                            int credits;
};

student::student()
{
            name = "No name yet";
            GPA = 0;
            credits = 0.0;
            cout << "Default constructor entered!" << endl;
}

student::student(string s, double gpa, int nCredits)
{
            name = s;
            GPA = gpa;
            credits = nCredits;
            cout << "Second constructor entered!" << endl;
 }

 void student::changeCredits(){
 cout << "Enter credits earned: ";
 cin >> credits;
 }

 int student::getCredits(){
   return credits;
 }

 void student::changeGPA(){
  cout << "Enter GPA: ";
  cin >> GPA;
 }

double student::getGPA(){
 return GPA;
 }

void student::displayStRec()
{
         cout << "   Name: " << name <<endl;
        cout << "    GPA: " << GPA <<endl;
        cout << "Credits: " << credits <<endl;
}

student::~student()
{
            cout << "Destructor entered!" << endl;
}

int main()
{
            student s1,s2("John",4.0,42);
            s2.changeCredits();
            s2.getCredits();
            s2.changeGPA();
            s2.getGPA();
            s2.displayStRec();
            return 0;
}

Answer 3

这是一个建议的解决方案，但我不知道你老师的命令：

！：将字符串添加到包含

2：仅使用会员数据而非非会员

3：要么使changeCredits和changeGPA取0参数，要求输入或输入外部并传递给它。

    #include <iostream>
#include <string>
using namespace std;

class student
{
    public:
        student();
        student(string s, double gpa, int nCredits);
        ~student(); //destructor

        void   changeCredits();
        int    getCredits();
        void   changeGPA();
        double getGPA();
        void   displayStRec();

    private:
        string name;
        double GPA;
        int    credits;
};

student::student() : 
    name("No name yet"), GPA(0.0), credits(0)
{
    cout << "Default constructor entered!" << endl;
}

student::student(string s, double gpa, int nCredits) : 
    name(s), GPA(gpa), credits(nCredits)
{
    cout << "Second constructor entered!" << endl;
}

void student::changeCredits()
{
    cout << "Enter credits earned:" << endl;
    cin  >> credits;
    cout << endl;
}

int student::getCredits()
{
    return credits;
}

void student::changeGPA()
{
    cout << "Enter GPA: " << endl;
    cin >> GPA;
    cout << endl;
}

double student::getGPA()
{
    return GPA;
}

void student::displayStRec()
{
    cout << "   Name: " << name <<endl;
    cout << "    GPA: " << GPA <<endl;
    cout << "Credits: " << credits <<endl;
}

student::~student()
{
    cout << "Destructor entered!" << endl;
}

int main()
{
    student s1, s2("John", 4.0, 42);
    s2.changeCredits();
    s2.getCredits();
    s2.changeGPA();
    s2.getGPA();
    s2.displayStRec();

    return 0;
}

范围和访问器功能与第二个构造函数？

3 个答案:

缺少s

缺少nCredits和gpa

哦，顺便说一句，这是毫无意义的

结论