c++ - Visual C++ 中的奇怪输出

Question

代码如下:

// WAP to implement student result preparation.

#include "stdafx.h"
#include "iostream"
#include "conio.h"

using namespace std;

float total;
const int obj = 3;
const int size = 3;

class student
{
    int rollno;
    char name[20], grade;
    float marks[size], perc;
public:
    void getval()
    {
        cout << "Enter roll number: ";
        cin >> rollno;
        cout << "\nEnter student's name: ";
        cin >> name;
        cout << "\nEnter student's physics marks: ";
        cin >> marks[0];
        cout << "\nEnter student's chemistry marks: ";
        cin >> marks[1];
        cout << "\nEnter student's mathematics' marks: ";
        cin >> marks [2];
        cout << "\n";
    }
    void calculate()
    {
        perc = total / 3;
        if (perc < 50)
            grade = 'F';
        else if (perc >=50 && perc < 60)
            grade = 'D';
        else if (perc >= 60 && perc < 75)
            grade = 'C';
        else if (perc >= 75 && perc < 90)
            grade = 'B';
        else
            grade = 'A';
    }
    void prnresult()
    {
        cout << "\nRoll number: " << rollno;
        cout << "\nName: " << name;
        cout << "\nTotal marks: " << total;
        cout << "\nPercentage: " << perc;
        cout << "\nGrade: " << grade;
        cout << "\n";
    }
};

student jk[obj];

int _tmain(int argc, _TCHAR* argv[])
{   
    for (int i = 0; i < obj; i++)
    {   cout << "Student " << i + 1 << "\n";
        jk[i].getval();
    }
    for (int j = 0; j < obj; j++)
    {
        jk[j].calculate();
        cout << "Result: ";
        jk[j].prnresult();
    }
    _getch();
    return 0;
}

这是一个教科书程序。作者说它在 Turbo C++ 中完美运行(你能想象吗？上次更新是在 1990 年代初期!)。但是当我在 Visual C++ 2010 Express 中编译它时，它不计算总数和百分比。它只是显示为零。知道为什么会这样吗？

Answer 1

作者撒谎。我在代码中找不到将任何值分配给 total 变量的任何位置。所以，total 值仍然是0(0 初始化全局变量)。因此 perc = total/3; 也等于 0。