从文本文件中的值减去，然后输出计算(C++)

Question

嗨，我正在处理一份工资申请，有四种选择，如下：

1.从商店银行帐户中减去一笔款项(该帐户是文本文件" shop ")。您不需要将相同的金额添加到另一个帐户中，但是您应该在一个单独的文件中使用时间戳记录事务。应用程序应防止帐户余额透支。

2.列出屏幕上最近的五项交易。如果还没有五笔交易，那就把它们都列出来。

3.将帐户名称、号码和当前余额打印到屏幕上。

4.退出程序。

我已经完成了1,3和4，但我完全不知道该怎么做，我希望有人能帮我解决这个问题。

int read_balance(void);
void write_balance(int balance);
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
    int selection;
    int total;
    int attempts = 0;
    string name;
    string number;
    cout << "Correct login details entered!"
         << "" << endl;
    cout << "1. Transfer an amount" << endl;
    cout << "2. List recent transactions" << endl;
    cout << "3. Display account details and current balance" << endl;
    cout << "4.Quit" << endl;
    cout << "Please enter menu number" << endl;
    cin >> selection;
    switch (selection)
    {
        case 1:
            cout << "How much do you wish to transfer?" << endl;
            int amount = 0;
            if (std::cin >> amount)
            {
                std::cout << "Transferred Amount:" << amount << "\n";
                int balance = read_balance();
                if (amount <= 0)
                {
                    std::cout << "Amount must be positive\n";
                }
                else if (balance < amount)
                {
                    std::cout << "Insufficient funds\n";
                }
                else
                {
                    int new_balance = balance - amount;
                    write_balance(new_balance);
                    std::cout << "New account balance: " << new_balance
                              << std::endl;
                    fstream infile("time.txt", ios::app);
                    std::time_t result = std::time(nullptr);
                    std::string timeresult = std::ctime(&result);
                    infile << amount << std::endl;
                    infile << timeresult << std::endl;
                }
            }
            break;
        case 2:
            cout << "Here are you're recent transactions" << endl;
            break;
        case 3:
            cout << "The account names is:" << name << endl;
            cout << "The account number is:" << number << endl;
            std::cout << "The current account balance is " << read_balance()
                      << std::endl;
            break;
        case 4:
            system("pause");
            return 0;
        default:
            cout << "Ooops, invalid selection!" << endl;
            break;
    }
    system("pause");
    return 0;
}
int read_balance(void)
{
    std::ifstream f;
    f.exceptions(std::ios::failbit | std::ios::badbit);
    f.open("shop.txt");
    int balance;
    f >> balance;
    f.close();
    return balance;
}
void write_balance(int balance)
{
    std::ofstream f;
    f.exceptions(std::ios::failbit | std::ios::badbit);
    f.open("shop.txt");
    f << balance;
    f.close();
}

Answer 1

在你的第二个开关箱里应该这样做：

case 2:
{
    std::cout << "Here are your recent transactions" << '\n';

    for (int i = 0, size = v.size(); i < (size <= 5 ? size : 5); ++i)
    {
        std::cout << i << ". " << v.at(i) << '\n';
    }

    break;
}