Question

结构问题1.cpp

    // Struct Problem 1.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include "structs.h"

double calculateEarnings(Advertising aDay);
void displayEarnings(int questionInstance, Advertising aDay);
void mainQuestions();

int _tmain(int argc, _TCHAR* argv[])
{
    mainQuestions();
    return 0;
}

double calculateEarnings(Advertising aDay)
{
    std::cout << aDay.usersClicked; //debug
    return aDay.totalAdsShown * aDay.usersClicked * aDay.averagePerAd;
}

void takeInData(int questionInstance, Advertising aDay)
{
    if (questionInstance == 0)
    {
        std::cin >> aDay.totalAdsShown;
    }
    else
        if (questionInstance == 1)
        {
            std::cin >> aDay.usersClicked;
        }
        else
            if (questionInstance == 2)
            {
                std::cin >> aDay.averagePerAd;
            }
    std::cin;
}

void mainQuestions()
{
    static Advertising aToday;
    aToday.totalAdsShown = 0;
    aToday.usersClicked = 0.00;
    aToday.averagePerAd = 00.00;

    std::cout << "Welcome! Please input the advertising data for today." << "\n";
    std::cout << "How many ads were shown today?" << "\n";
    takeInData(0, aToday);
    std::cout << "What percentage of users clicked our ads? (decimal form)" << "\n";
    takeInData(1, aToday);
    std::cout << "What were the average earnings per ad? (ex: 5.15)" << "\n";
    takeInData(2, aToday);

structs.h

    #ifndef STRUCTS_H
#define STRUCTS_H

typedef double percentage;
typedef double USD;

struct Advertising
{
    int totalAdsShown;
    percentage usersClicked;
    USD averagePerAd;
};

#endif

基本上，当被“cin”调用时，不会保存数据。我添加了一行来打印aDay.usersClicked值并打印到0.我正在学习c ++，所以问题非常基础。我很感激所有提示！

谢谢

Answer 1

改变这个：

void takeInData(int questionInstance, Advertising aDay)

进入这个：

void takeInData(int questionInstance, Advertising& aDay)

它会起作用。原因是在您的版本中，参数aDay是按值传递的;即参数的副本被传递给函数。因此takeInData()对其aDay版本所做的任何操作都在副本中完成。 takeInData()返回后，副本（及其中的信息）将丢失。

在已编辑的版本中，对aDay的引用将传递给该函数。现在它将引用传递的变量，即main()中的变量。现在takeInData()所做的所有事情都存储在main()中实际声明的值中。

（C ++）与结构和函数参数有关的简单问题

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