CIN循环永远不会终止

Question

我很难在程序中终止我的CIN循环。我的程序使用Linux重定向来读取文件HW07DATA的输入，数据文件看起来像：

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点，下一行是学生ID编号，其得分是-1终止。

。

我的问题：当我运行命令 ./a.out＆lt时，我的时循环永远不会终止。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！

#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 1002nn";
    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;
}

输出继续要求新输入。

Answer 1

您可能会在此找到答案，直到CIN中的cin中读取cin in c

因此，您可以使用getline通过行读取cin，然后分析所得的行，例如：

#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;
}

编辑：不要忘记检查解析结果并为任何故障进行流状态！

Answer 2

您应该始终检查输入是否成功：

if (std::cin >> TmpVal) {
    // do simething with the read value
}
else {
    // deal with failed input
}

如果失败，您晚上想检查eof()，以诱导失败是由于输入结束而导致的。

要处理错误，请查看std::istream::clear()和std::istream::ignore()。