c++ - 从同一类中的另一个方法调用方法时出错

Question

我似乎无法弄清楚我正在尝试构建的这个 GPA 计算器程序发生了什么。问题出在 Student 类的 printTranscript 方法中。该方法调用同一个类的getGPA方法，它返回一个double，输出的是一些海量数字而不是一个标准的GPA。

主要.cpp:

#include <iostream>
#include "Student.cpp"
using namespace std;
int main(){
    Student stud("Lebron", 23232);
    stud.addCourse("Passing", 3, 'A');
    stud.addCourse("Finals Record", 4, 'D');
    stud.printTranscript();
    return 0;
}

学生.h:

#include "Course.h"
#include <vector>
class Student{
private:
    string name;
    int studentID;
    vector<Course> courses;
public:
    Student(){
        name = "No Name";
        studentID = 0;
    }
    Student(string n, int ID){
        name = n;
        studentID = ID;
    }
    string getName(){
        return name;
    }
    void setName(string n){
        name = n;
    }
    int getID(){
        return studentID;
    }
    void setID(int ID){
        studentID = ID;
    }
    void addCourse(string, int, char);
    void addCourse(Course);
    double getGPA();
    void printTranscript();
};

学生.cpp:

#include "Student.h"
void Student::addCourse(string name, int credits, char grade){
    courses.push_back(Course(name,credits,grade));
}
void Student::addCourse(Course c){
    courses.push_back(c);
}
double Student::getGPA(){
    double gradePoints, totalCredits;
    for(int i = 0; i < courses.size(); i++){
        if(courses[i].getGrade() == 'A'){
            gradePoints += (4.0 * courses[i].getCredits());
            totalCredits += courses[i].getCredits();
        }
        else if(courses[i].getGrade() == 'B'){
            gradePoints += (3.0 * courses[i].getCredits());
            totalCredits += courses[i].getCredits();
        }
        else if(courses[i].getGrade() == 'C'){
            gradePoints += (2.0 * courses[i].getCredits());
            totalCredits += courses[i].getCredits();
        }
        else if (courses[i].getGrade() == 'D'){
            gradePoints += (1.0 * courses[i].getCredits());
            totalCredits += courses[i].getCredits();
        }
    }
    return (gradePoints / totalCredits);
}
void Student::printTranscript(){
    cout << "Transcript for: " << name << endl;
    cout << "============================" << endl;
    for(int i = 0; i < courses.size(); i++){
        cout << "Course: " << courses[i].getID() << endl;
        cout << "Grade: " << courses[i].getGrade() << endl;
        cout << endl;
    }
    cout << "Overall GPA: " << getGPA() << endl;
}

类(class).h:

#include <iostream>
#include <string>
using namespace std;
class Course{
private:
    string courseID; // Course name
    int numCredits; // Instructor
    char letterGrade; // Textbook
public:
    Course(string ID, int credits, char grade){ // Assign the course name.
        courseID = ID;
        numCredits = credits;
        letterGrade = grade;
    }
    string getID(){
        return courseID;
    }
    void setID(string ID){
        courseID = ID;
    }
    int getCredits(){
        return numCredits;
    }
    void setCredits(int credits){
        numCredits = credits;
    }
    char getGrade(){
        return letterGrade;
    }
    void setGrade(char grade){
        letterGrade =  grade;
    }
};

抱歉代码太长了，但我似乎无法弄清楚为什么 main 中的输出会给我:

Transcript for: Lebron James
============================
Course: Passing
Grade: A

Course: Finals Record
Grade: D

Overall GPA: 2.2321e+230

如果我在主类中 cout stud.getGPA 作为一个单独的语句，它工作正常。当从同一类的另一个方法调用时，如何解释此处输出的大量数字，这是如何解决的？

抱歉，代码太长了，但我不想错过任何东西，因为我仍处于 C++ 的初级阶段。

Answer 1

来自 dcl.init/7 :

To default-initialize an object of type T means:

• If T is a (possibly cv-qualified) class type, constructors are considered. The applicable constructors are enumerated ([over.match.ctor]), and the best one for the initializer () is chosen through overload resolution. The constructor thus selected is called, with an empty argument list, to initialize the object.

• If T is an array type, each element is default-initialized.

• Otherwise, no initialization is performed.

你直接在做一些操作+=:

totalCredits += courses[i].getCredits();

但是忘了初始化变量。不要假设所有内容最初都会设置为 零。

因此，将 totalCredits 初始化为 0.0。

添加-Wuninitialized:

按照@1201ProgramAlarm 的建议，使用-Wuninitialized 标记未初始化的变量。

warning: 'totalCredits' may be used uninitialized in this function [-Wuninitialized]

如果您想将警告视为错误，只需添加标志 -Werror