C++ 求数组中类型 x 价格的总和

Question

我被困在这个程序中，我要计算所有 CarType 的价格总和。 例如。福特的价格总和是 __。数据是从名为 input.dat 的文件中提取的。 我一生都无法弄清楚如何对某种汽车类型的所有元素进行分组并将总和相加，然后将总和存储到数组 carPriceSum 中。我了解如何找到数组中连续元素的总和。任何提示或示例将不胜感激！

    // carstats.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <string>
#include <conio.h> // I understand this is not best practice
#include <fstream>
using namespace std;

enum CarType
{
    Ford,
    Chevy,
    Honda,
    Toyota
};

struct CarCustomer
{
    string firstName;
    string lastName;
    double price;
    CarType carType;
};

void calcCarStats(CarCustomer arrCustomers[], int count, int carCount[], double carPriceSum[])
{
    for(int index = 0; index < count; index++)
    {
        carCount[arrCustomers[index].carType]++;
        carPriceSum[index] = arrCustomers[index].price;
        // This is where I'm stuck
    }
} 

void displayCarTypeCounts(int carCount[], double carPriceSum[])
{
    for(int index = Ford; index <= Toyota; index++)
    {
        cout << carCount[index] << " " << carPriceSum[index] << endl;
    }
}

int _tmain(int argc, _TCHAR* argv[])
{
    int count = 0;
    CarCustomer arrCustomers[100]; //Array of structs for the Struct CarCustomer
    CarCustomer carCustomer;
    int carCount[100] = {0};
    double carPriceSum[100] = {0.0};
    double carPriceAvg[100] = {0.0};
    ifstream fin;
    CarType carType; //CarType enum

    fin.open("input.dat");

    if(!fin)
    {
        cout << "Error opening file, check the file name" << endl;
        _getch();
        return -1;
    }

    while (!fin.eof())
    {
        int carTypeInt;

        fin >> arrCustomers[count].firstName;
        fin >> arrCustomers[count].lastName;
        fin >> arrCustomers[count].price;
        fin >> carTypeInt; 
        arrCustomers[count].carType = (CarType)carTypeInt;
        count++;
    }
    fin.close();

    calcCarStats(arrCustomers, count, carCount, carPriceSum);
    displayCarTypeCounts(carCount, carPriceSum);


    _getch();
    return 0;
}


    //input.dat
Joe Smith   5999.99 0
Mary    Doe 23999.99 1
Joe Green   1999.99 1
Jim Smith   4999.99 2
Jane    Green   3999.99 0
Mark    Doe 9999.99 1
John    Peters  7999.99 2
Jim Green   8999.99 3
Mindy   Doe 3999.99 2
Janet   Green   6999.99 1
Mork    Doe 2999.99 3
Jane    Smith   3999.99 3
John    Roberts 15999.99    1
Mandy   Doe 12999.99    0
Janet   Smith   6999.99 0
Macy    Doe 14999.99    1

Answer 1

我认为您只想添加到carPriceSum[n]中的“运行”总和：

从

更改 calcCarStats

    carCount[arrCustomers[index].carType]++;
    carPriceSum[index] = arrCustomers[index].price;
    // This is where I'm stuck

到

    CarType type = arrCustomers[index].carType;

    carCount[type]++;
    carPriceSum[type] += arrCustomers[index].price;

---

不相关的 cmets：

• 考虑改变 read 'eof()' 循环：

  CarCustomer current;
  int carTypeInt;
  while (fin >> current.firstName >> current.lastName >> current.price >> carTypeInt)
  {
      current.carType = (CarType)carTypeInt;
      arrCustomers[count] = current;
      count++;
  }
  

• 考虑在display 函数中打印实际车型：

  ostream& operator<<(ostream& os, CarType ct)
  {
      switch(ct)
      {
          case Ford:    return os << "Ford";
          case Chevy:   return os << "Chevy";
          case Honda:   return os << "Honda";
          case Toyota:  return os << "Toyota";
      }
      return os << "Unknown";
  }
  
  void displayCarTypeCounts(int carCount[], double carPriceSum[])
  {
      for(int index = Ford; index <= Toyota; index++)
      {
          cout << (CarType)index << " " << carCount[index] << " " << carPriceSum[index] << endl;
      }
  }
  

• 考虑使用标准库容器（地图、矢量）：查看演示Live on Coliru

  // carstats.cpp : Defines the entry point for the console application.
  //
  #include <iostream>
  #include <iomanip>
  #include <string>
  #include <vector>
  #include <map>
  #include <fstream>
  using namespace std;
  
  enum CarType
  {
      Ford,
      Chevy,
      Honda,
      Toyota
  };
  
  struct Stats
  {
      unsigned units_sold;
      double total_turnover;
      Stats() : units_sold(0), total_turnover(0.0) {}
  };
  
  typedef map<CarType, Stats> Statistics;
  
  ostream& operator<<(ostream& os, CarType ct) {
      switch(ct) {
          case Ford:    return os << "Ford";
          case Chevy:   return os << "Chevy";
          case Honda:   return os << "Honda";
          case Toyota:  return os << "Toyota";
      }
      return os << "Unknown";
  }
  
  struct CarCustomer
  {
      string firstName;
      string lastName;
      double price;
      CarType carType;
  };
  
  Statistics calcCarStats(vector<CarCustomer> const& arrCustomers)
  {
      Statistics stats;
      for (auto& customer : arrCustomers)
      {
          auto& entry = stats[customer.carType];
  
          entry.units_sold     += 1;
          entry.total_turnover += customer.price;
      }
  
      return stats;
  } 
  
  void displayCarTypeCounts(Statistics const& stats)
  {
      for (auto& entry: stats)
          cout << (CarType)entry.first << " " << entry.second.units_sold << " " << entry.second.total_turnover << endl;
  }
  
  int main()
  {
      vector<CarCustomer> arrCustomers;
      ifstream fin("input.dat");
  
      if(!fin)
      {
          cout << "Error opening file, check the file name" << endl;
          return -1;
      }
  
      CarCustomer current;
      int carTypeInt;
      while (fin >> current.firstName >> current.lastName >> current.price >> carTypeInt)
      {
          current.carType = (CarType)carTypeInt;
          arrCustomers.push_back(current);
      }
      fin.close();
  
      auto stats = calcCarStats(arrCustomers);
      displayCarTypeCounts(stats);
  }
  

Answer 2

最简单的做法（但不是最有效的）是遍历 arrCustomers 以查找特定的汽车类型并累积您的总和。如果您将该代码放在一个函数中，那么您可以为每种汽车类型调用它。