C ++的初學者。 幫助將結構傳遞給功能…？

Question

嗨，初學者程序員在這里：]甚至不知道如何表達這個問題。 我正在做家庭作業，似乎無法更改我創建的該結構的值（budget2）。

該程序的目標是顯示第一個結構budget1，並在用戶輸入budget2的值后找到它與budget2之間的差異。

根據調試器的說明，當我使用inputData函數輸入它們時，我並沒有更改budget2中的任何值，因此，當showDiff函數運行時，它僅從budget1中減去budget2中的每個值，使所有總計顯示為0。

#include <iostream>
#include <windows.h>
#include <string>

using namespace std;


struct MonthlyBudget
{
    MonthlyBudget();
    double housing, utilities, householdExpenses, transportation, food, medical, insurance, entertainment, clothing, misc;

};


int main()
{
    HANDLE screen = GetStdHandle(STD_OUTPUT_HANDLE);
    COORD position;

    void inputData(struct MonthlyBudget data);
    void displayData(struct MonthlyBudget);
    void showDiff(struct MonthlyBudget, struct MonthlyBudget); 
    struct MonthlyBudget budget1, budget2;


    displayData(budget1);
    inputData(budget2);
    showDiff(budget1, budget2);




    system ("PAUSE");
    return 0;
}

MonthlyBudget::MonthlyBudget()
{
    housing = 500.00;
    utilities = 150.00;
    householdExpenses = 65.00;
    transportation = 50.00;
    food = 250.00;
    medical = 30.00;
    insurance = 100.00;
    entertainment = 150.00;
    clothing = 75.00;
    misc = 50.00;
}

void displayData(struct MonthlyBudget data)
{
    cout << "\n\tBudget\n\n\t";
    cout << "$" << data.housing << "\n\n\t";
    cout << "$" << data.utilities << "\n\n\t";
    cout << "$" << data.householdExpenses << "\n\n\t";
    cout << "$" << data.transportation << "\n\n\t";
    cout << "$" << data.food << "\n\n\t";
    cout << "$" << data.medical << "\n\n\t";
    cout << "$" << data.insurance << "\n\n\t";
    cout << "$" << data.entertainment << "\n\n\t";
    cout << "$" << data.clothing << "\n\n\t";
    cout << "$" << data.misc << "\n\n\t";

}

void inputData(struct MonthlyBudget data)
{

    HANDLE screen = GetStdHandle(STD_OUTPUT_HANDLE);
    COORD position;

    position.X = 15;
    position.Y = 3;
    SetConsoleCursorPosition(screen, position);

    cin >> data.housing;
    position.Y = 5;
    SetConsoleCursorPosition(screen, position);

    cin >> data.utilities;
    position.Y = 7;
    SetConsoleCursorPosition(screen, position);

    cin >> data.householdExpenses;
    position.Y = 9;
    SetConsoleCursorPosition(screen, position);

    cin >> data.transportation;
    position.Y = 11;
    SetConsoleCursorPosition(screen, position);

    cin >> data.food;
    position.Y = 13;
    SetConsoleCursorPosition(screen, position);

    cin >> data.medical;
    position.Y = 15;
    SetConsoleCursorPosition(screen, position);

    cin >> data.insurance;
    position.Y = 17;
    SetConsoleCursorPosition(screen, position);

    cin >> data.entertainment;
    position.Y = 19;
    SetConsoleCursorPosition(screen, position);

    cin >> data.clothing;
    position.Y = 21;
    SetConsoleCursorPosition(screen, position);

    cin >> data.misc;
    position.Y = 23;
    SetConsoleCursorPosition(screen, position);

}


void showDiff(struct MonthlyBudget data, struct MonthlyBudget data2)
{   
    HANDLE screen = GetStdHandle(STD_OUTPUT_HANDLE);
    COORD position;

    position.X = 20;
    position.Y = 3;
    SetConsoleCursorPosition(screen, position);

    cout << (data.housing - data2.housing);

    position.Y = 5;
    SetConsoleCursorPosition(screen, position);
    cout << (data.utilities - data2.utilities);


    position.Y = 7;
    SetConsoleCursorPosition(screen, position);
    cout << (data.householdExpenses - data2.householdExpenses);

    position.Y = 9;
    SetConsoleCursorPosition(screen, position);
    cout << (data.transportation - data2.transportation);

    position.Y = 11;
    SetConsoleCursorPosition(screen, position);
    cout << (data.food - data2.food);

    position.Y = 13;
    SetConsoleCursorPosition(screen, position);
    cout << (data.medical - data2.medical);

    position.Y = 15;
    SetConsoleCursorPosition(screen, position);
    cout << (data.insurance - data2.insurance);

    position.Y = 17;
    SetConsoleCursorPosition(screen, position);
    cout << (data.entertainment - data2.entertainment);

    position.Y = 19;
    SetConsoleCursorPosition(screen, position);
    cout << (data.clothing - data2.clothing);

    position.Y = 21;
    SetConsoleCursorPosition(screen, position);
    cout << (data.misc - data2.misc);

    position.X = 5;
    position.Y = 23;
    SetConsoleCursorPosition(screen, position);

}

不太確定我在做什么錯，任何幫助將不勝感激。 非常感謝你。

PS。 我知道我的代碼一定看起來很荒謬。

Answer 1

您正在按值傳遞結構。
這意味着，無論何時調用函數之一，結構都會被復制，然后傳遞給函數。 因此，在您的情況下， budget2被復制並傳遞給inputData 。 但之后你inputData完成budget2作為功能上的復制工作還是一樣。
您需要通過指針或引用傳遞您的結構。 我希望在您的情況下使用參考。 因此，您的函數應如下所示：
void inputData(MonthlyBudget& data);

BTW：
您確實應該讀一本關於c ++的好書，並閱讀有關按值傳遞或按引用傳遞的知識。