Question

我遇到的问题是我不知道如何从已创建的文本文件中读取特定数字，并在程序的早期输入了值。

我希望在读取quizes的值之后使用嵌套循环语句读取值我需要将值加起来并将它们平均化，这需要多次发生

#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>

using namespace std;

int main()
{
    string StudentGrades;
    int studentID;
    double quiz1;
    double quiz2;
    double quiz3;
    double quiz4;
    double total=0;
    double choice;
    ofstream outFile;   

    cout << "Enter student ID number, Quiz 1 Grade, Quiz 2 Grade , Quiz 3 Grade, Quiz 4 Grade" << endl;
    outFile.open("StudentGrades.txt");
    //while (outFile.open)
    //{
        for (int x = 0; x < 4; x++)
        {
            cout << "Enter student ID: ";
            cin >> studentID;
            cout << "Enter quiz grade 1: ";
            cin >> quiz1;
            //cout << quiz1;
            cout << "Enter quiz grade 2: ";
            cin >> quiz2;
            //cout << quiz2;
            cout << "Enter quiz grade 3: ";
            cin >> quiz3;
            //cout << quiz3;
            cout << "Enter quiz grade 4: ";
            cin >> quiz4;
            //cout << quiz4;
            cout << endl;
            //outFile.open("StudentGrades.txt");
            if (outFile.is_open())
            {
                cout << "inside if/else outFile" << endl;
                //outFile << "File successfully open";

                outFile << studentID << " " << quiz1 << " " << quiz2 << " " << quiz3 << " " << quiz4 << endl;

            }
            else
            {
                cout << "Error opening file";
            }

            cout << "Enter 0 for no more students. Enter 1 for more students." << endl;
            cin >> choice;
            if (choice == 1)
                continue;
            if (choice == 0)
            {
                outFile.close();
                break;
            }

        }

    //}
    //declaring file and opening it






        ifstream inFile;
        inFile.open("StudentGrades.txt");

        while (inFile>>studentID)
        {
            cout << studentID<< quiz1 <<quiz2<<quiz3<<quiz4<< endl;
        }



    system("pause");
    return (0);
}

Answer 1

您没有阅读输入文件中的所有字段，而只是阅读studentID。

while (inFile>>studentID)
{
    cout << studentID<< quiz1 <<quiz2<<quiz3<<quiz4<< endl;
}

尝试：

while (inFile >> studentID >> quiz1 >> quiz2 >> quiz3 >> quiz4)
{
    cout << studentID << quiz1 << quiz2 << quiz3 << quiz4 << endl;
}

<强>更新

以下是我对重构程序的建议。创建执行特定任务的函数然后从更高级别的函数调用它们而不是将它们全部集中在一个大函数中是很好的。

#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>

using namespace std;

void saveStudentData(string const& filename)
{
   int studentID;
   double quiz1;
   double quiz2;
   double quiz3;
   double quiz4;

   // Use int type for choice, not double
   int choice;

   ofstream outFile(filename);
   if (!outFile.is_open())
   {
      // Problem opening file.
      cout << "Error opening file";
      return;
   }

   cout << "Enter student ID number, Quiz 1 Grade, Quiz 2 Grade , Quiz 3 Grade, Quiz 4 Grade" << endl;
   for (int x = 0; x < 4; x++)
   {
      cout << "Enter student ID: ";
      cin >> studentID;
      cout << "Enter quiz grade 1: ";
      cin >> quiz1;
      cout << "Enter quiz grade 2: ";
      cin >> quiz2;
      cout << "Enter quiz grade 3: ";
      cin >> quiz3;
      cout << "Enter quiz grade 4: ";
      cin >> quiz4;
      cout << endl;

      outFile << studentID << " " << quiz1 << " " << quiz2 << " " << quiz3 << " " << quiz4 << endl;

      cout << "Enter 0 for no more students. Enter 1 for more students." << endl;
      cin >> choice;
      if (choice == 0)
      {
         break;
      }
   }
}

void readStudentData(string const& filename)
{
   int studentID;
   double quiz1;
   double quiz2;
   double quiz3;
   double quiz4;
   double total=0;

   ifstream inFile(filename);
   while (inFile >> studentID >> quiz1 >> quiz2 >> quiz3 >> quiz4)
   {
      total = (quiz1 + quiz2 + quiz3 + quiz4); 
      cout << studentID << " " << quiz1 << " " << quiz2
           << " " << quiz3 << " " << quiz4 << " " << total << endl;
   }
}

int main()
{
   string filename("StudentGrades.txt");
   saveStudentData(filename);
   readStudentData(filename);
   return (0);
}

如何从txt文件C ++中读取特定数字

1 个答案: