C++编程:作业的输出是边缘关闭的

Question

好的,所以分配是从名为tickets.txt的文件中获取输入,并输出已售票的总数以及总收入.文本文件中的值输入两列(1)售出的票数,以及(2)每种票类的价格.

文本文件如下所示:

250 5750
100 28000
50 35750
25 18750

这是我想出的代码......

#include <iostream>
#include <fstream>
#include <iomanip>
using namespace std;

/* Program Name:  Ticket_Sales.cpp
 * Date: May 2, 2018
 * Purpose: Calculate Total Ticket Sales
 */

int main() {

    {
        ifstream inFile;
        float ticket_cost;
        float tickets_sold;
        float total_cost ;
        float total_sold ;
        float ticket_revenue;

        /*
         * I noticed someone doing something similar to this on StackExchange; seems absolutely brilliant to include
         * a manner to check if the program is accessing the file.
         */
        inFile.open("C:\\Users\\pinkp\\CLionProjects\\M05_Ticket_Sales\\tickets.txt");
            if (inFile.fail()) {
                cout << "Failed to open the file." << endl;
                cin.get ();
                return 1;
            }

        while(inFile >> tickets_sold >> ticket_cost) {
                total_sold += tickets_sold;
                total_cost += ticket_cost;
                ticket_revenue = (total_cost * total_sold);

        }
        cout << fixed << setprecision(2);
        cout << "Total Tickets Sold:  " << total_sold << "." << endl;
        cout << "Total Revenue:  " << ticket_revenue << "." << endl;
    }
    /*
     * The value continues to return 2 less than the intended output, and I cannot pinpoint the exact cause.
     */
    return 0;
}

但是我对ticket_revenue的输出继续给我37506248.00,当手动将数字输入计算器时会给你37506250.00.两个数字的差异.我想过只做一个'+2'来得到正确的数字,但我认为我的教授会对此不以为然.

无论ticket.txt中的数字(我已经改变了几次),它总是比我期望的少两个.这是一些超级简单的C++或编程概念,我不知何故错过了吗？

谢谢!

Answer 1

您无法初始化ticket_revenue- 并查看它是如何分配的:

            ticket_revenue = (total_cost * total_sold);

这将覆盖ticket_revenue与该产品总销售的门票数量和金额所有的价格.

你需要像(未经测试的):

    unsigned long total_sold = 0;
    unsigned long ticket_revenue = 0;
    while (inFile >> tickets_sold >> ticket_cost) {
            auto transaction_revenue = tickets_sold * ticket_cost;
            total_sold += tickets_sold;
            ticket_revenue += transaction_revenue;
    }

顺便说一句,不要使用浮点类型进行货币计算!

这是一个修复了上述错误的代码版本,没有外部输入文件(因此它代表了一个Minmal,Complete和Verifiable示例):

#include <iostream>
#include <vector>

int main()
{
    static const
        std::vector<std::pair<int, long>> sales =
        {{ 250, 5750 },
         { 100, 28000 },
         { 50, 35750 },
         { 25, 18750 } };

    long total_sold = 0;
    long ticket_revenue = 0;

    for (auto& sale: sales) {
        int tickets_sold = sale.first;
        long ticket_cost = sale.second;
        total_sold += tickets_sold;
        ticket_revenue += tickets_sold * ticket_cost;
    }

    std::cout << "Total Tickets Sold:  " << total_sold << ".\n";
    std::cout << "Total Revenue:  " << ticket_revenue << ".\n";
}

这产生了正确的答案:

Total Tickets Sold:  425.
Total Revenue:  6493750.