介绍性 C++：将字符串与文件行中的数字分开并将这些数字相加

Posted 2023-02-21

【中文标题】介绍性 C++：将字符串与文件行中的数字分开并将这些数字相加

【英文标题】：Introductory C++: Separating strings from digits in a file line and summing up those digits

【发布时间】：2016-04-01 03:06:17

【问题描述】：

我是 C++ 新手，正在编写一个本质上是成绩册的程序，其中给我一个包含学生的文件和他们的成绩列表。以下是文件外观的示例：

“约翰·史密斯 34 29 10 49

汉娜·琼斯 45 48 34 46"

等等

所有成绩都满分 50。我必须创建两个向量，一个用于姓名，一个用于每个学生的分数总和（他们的成绩百分比）。向量按最高等级排序。我想我已经弄清楚了这部分并为它创建了一个函数。

我不知道如何将分数的总和相加。我知道我需要将名称与文件中的数字分开，然后为文件中的每一行添加这些数字。我只是不知道我将如何去做。我尝试了一些事情，但它还没有奏效。到目前为止，这是我的代码：

#include <iostream>;
#include <vector>;
#include <fstream>;
#include <string>;
#include <sstream>;
using namespace std; 

void sort_vectors(vector<string>& n, vector<double>& p)

// selection sort algorithm 
// sorting the percentages 
for (int i = 0; i < p.size() - 1; i++)

    int min = i;
    for (int j = i + 1; j < p.size(); j++)
    
        if (p[j] < p[min])
        
            min = j; 
        
    
    int temp = p[i];
    string ntemp = n[i];
    p[i] = p[min];
    p[min] = temp; 
    n[i] = n[min];
    n[min] = ntemp; 
    


char percent2grade(double p)

    if (p >= 90)
        return 'A';
    else if (90 > p >= 80)
        return 'B';
    else if (80 > p >= 70)
        return 'C';
    else if (70 > p >= 60)
        return 'D';
    else
        return 'E'; 


int main()

// Ask the user for a filename and open the file in read mode. 
    cout << "Please enter a file name + .txt: ";
    string filename;
    cin >> filename;
    ifstream in_file;
    in_file.open(filename);

//While file DNE
    while (in_file.fail())
    
    //ask user to enter valid filename until user enters valid filename.
        in_file.clear();
        cout << "This file doesn't exist. Please enter a valid file name + .txt: ";
        cin >> filename;
        in_file.open(filename);
    
    //Creating a new file
    ofstream out_file;
    out_file.open("output.txt");

    //Creating the vectors and string for reading the file 
    vector<string> students;
    vector<double> grades; 
    string line; 
    //reading the file one line at a time
    while (getline(in_file, line))
    
        string name; 
        double score; 

    // Splitting the lines between names and grades
    //locate the first digit 
        int i = 0; 
        while (!isdigit(line[i]))
        
            i++;
        
        //Locate the end of the name
        int j = i - 1; 
        while (isspace(line[j]))
        
            j--;
        
        // Extract name
        name = line.substr(0, j + 1);
        students.push_back(name);

       // Extract grades
       istringstream stream;
       stream.str(line.substr(i));
       // As you can see here, I tried to make an array.
       // It didn't exactly work, but I'll leave it this way for now. 
       const int CAPACITY = 100; 
       double gradesum[CAPACITY];
       for (int k = 0; k < (line.substr(i)).size(); k++)
       
            stream >> gradesum[k];
            score = gradesum[k]; 
       
     

     system("pause");
    return 0; 
 

所以，如您所见，我尝试创建一个数组并将名称后的所有数字都放入数组中。我还没有尝试将它们加在一起，但我想看看当我看到数组时是否可以。这不好。看起来真的很丑。我完全迷路了，所以如果有人可以帮助我，我会非常感激。

我意识到我的代码中的错误可能比我预期的要多，但我现在正在尽力而为！如果您看到任何其他可以改进的地方，请告诉我。

谢谢。

【参考方案1】：

#include <iostream>
#include <vector>
#include <fstream>
#include <string>
#include <sstream>
using namespace std; 

void sort_vectors(vector<string>& n, vector<double>& p)

// selection sort algorithm 
// sorting the percentages 
for (int i = 0; i < p.size() - 1; i++)

    int min = i;
    for (int j = i + 1; j < p.size(); j++)
    
        if (p[j] < p[min])
        
            min = j; 
        
    
    int temp = p[i];
    string ntemp = n[i];
    p[i] = p[min];
    p[min] = temp; 
    n[i] = n[min];
    n[min] = ntemp; 
    


char percent2grade(double p)

    if (p >= 90)
        return 'A';
    else if (90 > p >= 80)
        return 'B';
    else if (80 > p >= 70)
        return 'C';
    else if (70 > p >= 60)
        return 'D';
    else
        return 'E'; 


int main()

// Ask the user for a filename and open the file in read mode. 
    cout << "Please enter a file name + .txt: ";
    string filename;
    cin >> filename;
    ifstream in_file;
    in_file.open(filename.c_str());

//While file DNE
    while (in_file.fail())
    
    //ask user to enter valid filename until user enters valid filename.
        in_file.clear();
        cout << "This file doesn't exist. Please enter a valid file name + .txt: ";
        cin >> filename;
        in_file.open(filename.c_str());
    
    //Creating a new file
    ofstream out_file;
    out_file.open("output.txt");

    //Creating the vectors and string for reading the file 
    vector<string> students;
    vector<double> grades; 
    string line; 
    //reading the file one line at a time
    while (getline(in_file, line))
    
        string name; 
        double score; 

    // Splitting the lines between names and grades
    //locate the first digit 
        int i = 0; 
        while (!isdigit(line[i]))
        
            i++;
        
        //Locate the end of the name
        int j = i - 1; 
        while (isspace(line[j]))
        
            j--;
        
        // Extract name
        name = line.substr(0, j + 1);
        students.push_back(name);

       // Extract grades
       istringstream stream;
       stream.str(line.substr(i));

       // This gives you the mean score in percent
       int total=0;
       j=0;
       while(stream>>i)
        total+=i;
        j++;
       
       score=total*2/j;
     

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