c++ 多维排序

Question

我编写了一个基本程序，用于收集学生姓名和答案并自动为它们评分。最后，我想用相应的名称按降序对分数进行排序。我了解如何对分数进行排序，但不能与学生姓名结合使用。这是我目前所拥有的。

#include "stdafx.h"
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;


int _tmain(int argc, _TCHAR* argv[])
{
    //declare variables
    char choice;
    string studentName;
    vector<char> answers;
    vector<string> names;
    int getStudents();
    int getQuestions();

    //calls function to get number of questions
    int questions = getQuestions();

    //Get answers
    for (int i = 0; i < questions; ++i) {
        cout << "What is the answer for question " << i + 1 << endl;
        cin >> choice;
        answers.push_back(choice);
    }

    //Get number of students
    int students = getStudents();

    //Get student names
    for (int i = 0; i < students; i++) {
        cout << "Student " << i + 1 << ", what is your name?" << endl;
        cin >> studentName;
        names.push_back(studentName);
    }

    int score = 0;
    char studentAnswer;
    vector<char> userAnswer;
    vector<float> finalScore;

    //gets student answers
    for (int i = 0; i < students; i++) {
        score = 0;
        for (int j = 0; j < questions; j++) {
            cout << names[i] << ", what is your answer for question " << j + 1 << "?" << endl;
            cin >> studentAnswer;
            userAnswer.push_back(studentAnswer);
            if (userAnswer[i*questions+j] == answers[j])
                score = score + 1;
        }
        finalScore.push_back(score);
    }

    //outputs scores
    std::sort(finalScore.begin(), finalScore.end());
    for (int i = 0; i < students; i++) {
        cout << names[i] << " scored " << finalScore[i] << " out of " << questions <<
            " or " << (finalScore[i] / questions) * 100 << "%" << endl;
    }

    system("pause");
    return 0;
}

//function to get number of questions
int getQuestions()
{
    int questions;
    cout << "How many questions are there?" << endl;
    cin >> questions;
    return questions;
}

//function to get number of students
int getStudents()
{
    int students;
    cout << "How many students are there?" << endl;
    cin >> students;
    return students;
}

现在，它按降序对分数进行排序，但输出的分数名称不正确。

Answer 1

您需要以某种方式将学生姓名与他/她的分数“联系起来”。一个非常简单直接的方法是创建一个结构，即

typedef struct Student
{
    string student_name_;
    float student_score_;
} Student;

接下来，您需要定义一个比较函数（查看此处的示例：http://www.cplusplus.com/reference/algorithm/sort/），以便您可以使用std:sort 对Students 的向量进行排序。您的比较功能可能是这样的：

bool myCompareFunction ( Student a, Student b) 
{ 
    return (a.student_score_ < b.student_score_);
}

Answer 2

为了保持你正在做的事情的精神，你可以制作一个成对的向量，这是一个代码示例：

#include<vector>
#include<string>
#include<iostream>
#include<algorithm>

int main()
{
  std::vector< std::pair<double,std::string> > my_student_list; //  first element is the grade, second is the name
  std::pair<double,std::string>  student1(2.,"name1"),student2(2.,"name2"),student3(1.,"name3");
  my_student_list.push_back(student1);
  my_student_list.push_back(student2);
  my_student_list.push_back(student3);

  std::sort(my_student_list.begin(),my_student_list.end()); // sort by grade

  // loop over the vector to print the sorted list
  for(std::vector< std::pair<double,std::string> >::iterator iterator = my_student_list.begin(); iterator != my_student_list.end(); iterator++){
    // iterator->second is the name, and iterator->first the associated grade
    std::cout << iterator->second << " " << iterator->first << std::endl;
  }
  return 0;
}