c++ - 简单的 c++ ATM(不能存储余额变量输入)

Question

我正在制作一个简单的 c++ atm 程序，但我在存款或取款后无法更改余额。

// C++ ATM

#include "std_lib_facilities.h"

int main()
{
    bool card_is_inserted = false;
    double balance = 0.0;
    //double new_balance = balance;


    // HOME

    //Starts over if variable is false
    while (card_is_inserted == false)
    {
        cout << "Wellcome to Well's Fargo ATM " << '\n'
        << "Insert card Yes or No"<< endl;
        string request;
        getline(cin,request);

        // Function is needed for aceppting different no's and yes's
        //-=-=-=--=-==--=-=-==-==-=--==--=-=-
        // loads atm
        if (request == "yes")
        {
            cout << "Alright, Your current balance is:" << endl
            << balance << endl;
            card_is_inserted = true;
        }

        // home
        string option = "cancel";

        while (card_is_inserted == true)
        {
            cout << "Would you like to withdraw or deposit? (Cancel)"<< endl;
            getline(cin,option);

            double cash_ = 0;

            if (option == "deposit")
            {
                cout << "How much money would you like to deposit?" << endl;
                cin >> cash_;
                double new_deposit_balance = balance + cash_;

                cout << "You placed: $" << cash_ << endl
                    << "Your New Balance is: $" << new_deposit_balance << endl;
            }

            if (option == "withdraw")
            {
                cout << "How much money would you like to withdraw?" << endl;
                cin >> cash_;
                double new_witdraw_balance = balance - cash_;

                if(balance <= 0)
                {
                    cout << "You don't have: $" << cash_ << endl;
                }
                else
                {
                cout << "You toke: $" << cash_ << endl
                << "Your New Balance is: $"<< new_witdraw_balance << endl;
                }
            }

            if (option == "cancel")
            {
                cout << "Ok, bye" << endl;
                card_is_inserted = false;
            }
        }
    }
}

示例:我输入 yes 进行存款(或取款)，然后输入一个简单的 double，例如 12.50，然后它会显示我的当前余额为 12.50；之后，我想在 12.00 时提款，还剩 0.50。但我不能，因为余额变量没有存储我之前的值 12.50。我尝试制作“double new_balance = balance”，但无法像在 swift 中那样工作。

Answer 1

您没有将 balance 设置为 new_widraw_balance 或 new_deposit_balance。

double new_deposit_balance = balance + cash_; 没有设置 balance 值，因为你引入了 balance 的值，但是你没有将 balance + cash_ 的结果分配给 balance。

你需要在 cout 之后的每个 if 的末尾添加类似 balance = new_widraw_balance; 和 balance = new_deposit_balance; 的内容 语句。

if(option == "deposit")
{
    cout << "How much money would you like to deposit?" << endl;
    cin >> cash_;
    double new_deposit_balance = balance + cash_;

    cout << "You placed: $" << cash_ << endl << "Your New Balance is: $" << new_deposit_balance << endl;

    balance = new_deposit_balance; // this
}

if(option == "withdraw")
{
    cout << "How much money would you like to withdraw?" << endl;
    cin >> cash_;
    double new_witdraw_balance = balance - cash_;

    if(balance <= 0)
    {
        cout << "You don't have: $" << cash_ << endl;
    }
    else
    {
        cout << "You toke: $" << cash_ << endl << "Your New Balance is: $"<< new_witdraw_balance << endl;
        balance = new_witdraw_balance; // and this
    }