Cin 循环永不终止 [英] Cin loop never terminating

问题描述

我无法让我的 cin 循环在我的程序中终止.我的程序使用 Linux 重定向从文件 hw07data 中读取输入，数据文件如下所示:

I'm having trouble getting my cin loop to terminate in my program. My program uses Linux redirection to read in input from the file hw07data, the data file look like this:

100 20 50 100 40 -1 
A34F 90 15 50 99 32 -1
N12O 80 15 34 90 22 -1

第一部分是班级的总分，下一行是学生ID号和他们的分数，都以-1结束.

The first portion is the total points for the class, the next lines are the students ID number followed by their scores, all terminated by -1.

我的问题:当我运行命令 ./a.out < 时，我的 while 循环永远不会终止.hw07data，有人可以查看我的代码并给我一些提示吗?我不想要答案，因为这是作业，我只需要一些指导.谢谢！！

My issue: my while loop never terminates when i run the command ./a.out < hw07data, could anyone look over my code and give me some hints? I dont want the answer, as this is homework, i just need some guidance. Thanks!!

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

const int SENTINEL = -1;           //signal to end part of file
const int LTAB = 8;                //left tab
const int RTAB = 13;               //right tab

int main()
{
    cout << "Grant Mercer Assignment 7 Section 1002

";
    cout << setprecision(2) << fixed << showpoint;
    cout << left << setw(LTAB) << "ID CODE" <<
                right << setw(RTAB) << "POINTS" <<
                setw(RTAB) << "PCT" << setw(RTAB) <<
                 "GRADE" << endl;
    double Percentage,              //holds students percentage
           AvgPercentage;
    int Earnedpoints,               //earned points for specific student
        Totalpoints,                //total points possible for all students
        AvgPoints,                  //average points for all students
        NumClass;                   //counts the number of students
    Totalpoints = Earnedpoints =    //set all vals equal to zero
    AvgPoints = AvgPercentage = Percentage =  NumClass = 0;
                                    //first and last char for studentID
    char Fchar,Lchar, Num1, Num2, Grade;

    int TmpVal = 0;                 //temporary value
    cin >> TmpVal;
    while(TmpVal != -1)             //reading in TOTAL POINTS
    {
        Totalpoints += TmpVal;      //add scores onto each other
        cin >> TmpVal;              //read in next value
    }

    while(cin)                       //WHILE LOOP ISSUE HERE!
    {
                                     //read in student initials
            cin >> Fchar >> Num1 >> Num2 >> Lchar >> TmpVal;
            while(TmpVal != -1)
            {
                Earnedpoints += TmpVal; //read in points earned
                cin >> TmpVal;
            }
                                        //calculate percentage
            Percentage = ((double)Earnedpoints / Totalpoints) * 100;
            AvgPercentage += Percentage;
            NumClass++;
            if(Percentage >= 90)        //determine grade for student
                Grade = 'A';
            else if(Percentage >= 80 && Percentage < 90)
                Grade = 'B';
            else if(Percentage >= 70 && Percentage < 80)
                Grade = 'C';
            else if(Percentage >= 60 && Percentage < 70)
                Grade = 'D';
            else if(Percentage < 60)
                Grade = 'F';
                                        //display information on student


            cout << left << Fchar << Num1 << Num2 << setw(LTAB) << Lchar << right << setw(RTAB-3) << Earnedpoints <<
            setw(RTAB) << Percentage <<  setw(RTAB) << Grade << endl;
            TmpVal = Earnedpoints = 0;
    }
    AvgPercentage /= NumClass;
    cout << endl << left << setw(LTAB+20) << "Class size: " << right << setw(RTAB) << NumClass << endl;
    cout << left << setw(LTAB+20) << "Total points possible: " << right << setw(RTAB) << Totalpoints << endl;
    cout << left << setw(LTAB+20) << "Average point total: " << right << setw(RTAB) << AvgPoints << endl;
    cout << left << setw(LTAB+20) << "Average percentage: " << right << setw(RTAB) << AvgPercentage << endl;
}

输出继续要求新的输入.

The output continues to ask for new input.

推荐答案

你可以在那里找到答案 如何从C++中的cin读取到EOF

You may find answer there How to read until EOF from cin in C++

因此您可以使用 getline 逐行读取 cin 并解析结果行，如下所示:

So you can read cin line by line using getline and parse the resulting lines, like that:

#include <iostream>
#include <sstream>
#include <string>

int main() {
    int a, b;

    std::string line;
    while (std::getline(std::cin, line)) {
        std::stringstream stream(line);

        stream >> a >> b;
        std::cout << "a: " << a << " - b: " << b << std::endl;
    }

    return 0;
}

不要忘记检查解析结果和流状态是否有任何失败！

Do not forget to check parsing results and stream state for any failure!

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