如何从文件中读取并存储变量？

Question

我正在制作一个程序来计算学生的测验平均分和 class 平均分，同时使用循环来简化它并将数据存储到一个文件中（目前只是一个 .txt）。

我是 c++ 的新手，这可能是我迄今为止所做的最先进的事情...

我当前的代码是：

// Grade Average calculator

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

int main(){
    ofstream outputFile;
    ifstream inputFile;
    int continueYes;
    double  qz, score;
    string studentId;

    //Open File
    outputFile.open("quizav.txt");
    //Continue to start...
    cout << "Press 1 to add a student, Press 0 to exit.\n";
    cin >> continueYes;

    while (continueYes == 1){
        cout << "Please Enter student ID: ";
        cin >> studentId;

        outputFile << studentId << " ";

        for (qz = 1; qz < 5; qz++){
            cout << "Enter quiz score " << qz << " ";
            cin >> score;

            +-score;
            outputFile << " " << score << " ";
        }

        cout << "Press 1 to add a student, press 0 if no more.\n";
        cin >> continueYes;
        outputFile << " " << endl;

    }

    outputFile.close();

    //OUT PUT FINISHED
    double average;
    double student, studentInfo;
    inputFile.open("quizav.txt");

    while (inputFile >> studentInfo){

        cout << studentInfo << endl;
    }

    system("pause");
    return 0;
}

虽然上半部分工作正常，并且像这样将信息存储在文本文件中

student id  score, score, score
student id  score, score, score
etc.

我不确定如何在底部进行 while 和 for 循环以大致提供我想要的输出：

学生 1 的平均分：平均分学生 2 的平均水平：平均水平等等

class平均：

底部的当前 While/for 循环显示文件中的正确信息，只是不正确（学生 ID 之间没有间隙）

我真的需要它一次获取一行，取平均数，然后存储总数以便以后取平均数。

感谢您的帮助。

Answer 1

int i = 0;
while (inputFile >> studentInfo)
{
    cout << "Student " << i << "'s info is " << studentInfo << endl;
    ++i;
}

这是你要问的吗？

针对 OP 的评论进行了编辑。好的：所以您希望显示的信息是平均值。所以存储这个平均值是有意义的（如果这是你想要的）。您可以用以下代码替换 qz 上的循环，以实现此目的：

    double totalScore = 0.0;
    enum {NUM_QUIZZES = 5};

    //read in 5 quizzes and get the total score
    for (qz = 1; qz < 5; qz++)
    {
        cout << "Enter quiz score " << qz << " ";
        cin >> score;

        totalScore += score;
    }

    //print the average score to a file
    outputFile << " " << totalScore/NUM_QUIZZES << " ";

Answer 2

我在您现有的代码中添加了以下代码，在评论后"Output Finished"

double studentInfo;
inputFile.open("quizav.txt");

int count = 0, numstudents = 0, numquizzes = 4;
double studentScores = 0, studentAvg = 0, totalAvg = 0;
cout << endl << "Class Statistics" << endl << endl;

while (inputFile >> studentInfo){
    if(count == 0){         //if count == 0, then studentInfo contains the ID
        ++numstudents;      //increment number of students
        cout << "Current Student ID: " << studentInfo << endl;     //output student ID
    }
    else{                   //else, studentInfo contains a quiz score
        studentScores += studentInfo;       //total up cur student quiz scores
    }
    ++count;        //increment counter to keep track of which data your're looking at
    if(count == numquizzes + 1){        //if counter = number of quizzes + 1 for student ID, current student is now complete
        studentAvg = studentScores / numquizzes;    //compute the average for student
        totalAvg += studentAvg;         //add average to total for later class avg calculation
        studentScores = 0;              //reset scores for next student
        cout << "     Student Average: " << studentAvg << endl;     //output current student average
        count = 0;      //reset counter
    }
}
totalAvg = totalAvg/numstudents;        //when all students are evaluated, calc total average
cout << endl << "Class Average: " << totalAvg << endl;
inputFile.close();
return 0;

这是计算平均值的基本方法。该代码包含解释其工作原理的注释。

它一次保存一个学生的数据，计算读取所有学生数据时的平均值，继续计算直到所有学生都被占。

这是我指定输入的输出：

Class Statistics

Current Student ID: 123
     Student Average: 5
Current Student ID: 234
     Student Average: 4.25
Current Student ID: 568
     Student Average: 4

Class Average: 4.41667

如何从文件中读取并存储变量？

How to read from a file and store variables?

c++

for-loop

file

getline

while-loop