基于C++的个人银行账户管理系统 ： 设计一个面向个人的银行账户管理系统， 包括设置账号、余额、年利率等信息，还包括显示信息、存款、取款、结算利息等操作。要求： （1）无论是存款、取款还是结算利息，都需要修改当前的余额并且将余额的变动输出。 （2）实现利息计算。由于账户的余额是不断变化的，因此不能同过余额与年利率相乘的办法来计算年利，而是需要将一年中每天的余额累计起来再除以一年的总天数。 （3）在个人银行账户管理程序中增加信用卡账户。 （4）输出不同账户信息。 （5）将所有用户信息存于文件中。

以下是一个基于C++的个人银行账户管理系统的示例代码，其中包括一个账户类（Account）和一个信用卡账户类（CreditAccount）：

#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
#include <ctime>

using namespace std;

class Account {
private:
    string accountNumber;
    double balance;
    double annualInterestRate;

public:
    Account(string accountNumber, double balance, double annualInterestRate) {
        this->accountNumber = accountNumber;
        this->balance = balance;
        this->annualInterestRate = annualInterestRate;
    }

    string getAccountNumber() {
        return accountNumber;
    }

    double getBalance() {
        return balance;
    }

    double getAnnualInterestRate() {
        return annualInterestRate;
    }

    void deposit(double amount) {
        balance += amount;
        cout << "Deposit $" << fixed << setprecision(2) << amount << " successfully. Current balance is $" << fixed << setprecision(2) << balance << endl;
    }

    void withdraw(double amount) {
        if (balance >= amount) {
            balance -= amount;
            cout << "Withdraw $" << fixed << setprecision(2) << amount << " successfully. Current balance is $" << fixed << setprecision(2) << balance << endl;
        } else {
            cout << "Withdraw failed. Not enough balance." << endl;
        }
    }

    double calculateInterest() {
        time_t now = time(0);
        tm* ltm = localtime(&now);
        int days = ((ltm->tm_year + 1900) % 4 == 0 && (ltm->tm_year + 1900) % 100 != 0) || (ltm->tm_year + 1900) % 400 == 0 ? 366 : 365;
        double dailyBalance = balance / days;
        double annualInterest = dailyBalance * annualInterestRate;
        cout << "The annual interest is $" << fixed << setprecision(2) << annualInterest << endl;
        return annualInterest;
    }
};

class CreditAccount : public Account {
private:
    double creditLimit;
    double debt;
    double debtInterestRate;

public:
    CreditAccount(string accountNumber, double balance, double annualInterestRate, double creditLimit, double debt, double debtInterestRate) : Account(accountNumber, balance, annualInterestRate) {
        this->creditLimit = creditLimit;
        this->debt = debt;
        this->debtInterestRate = debtInterestRate;
    }

    double getCreditLimit() {
        return creditLimit;
    }

    double getDebt() {
        return debt;
    }

    double getDebtInterestRate() {
        return debtInterestRate;
    }

    void overdraft(double amount) {
        if (amount > creditLimit - debt) {
            cout << "Overdraft failed. Exceed the credit limit." << endl;
        } else {
            debt += amount;
            cout << "Overdraft $" << fixed << setprecision(2) << amount << " successfully. Current debt is $" << fixed << setprecision(2) << debt << endl;
        }
    }

    void repayment(double amount) {
        if (amount > debt) {
            cout << "Repayment failed. The amount is greater than the debt." << endl;
        } else {
            debt -= amount;
            cout << "Repayment $" << fixed << setprecision(2) << amount << " successfully. Current debt is $" << fixed << setprecision(2) << debt << endl;
        }
    }

    double calculateInterest() {
        time_t now = time(0);
        tm* ltm = localtime(&now);
        int days = ((ltm->tm_year + 1900) % 4 == 0 && (ltm->tm_year + 1900) % 100 != 0) || (ltm->tm_year + 1900) % 400 == 0 ? 366 : 365;
        double dailyDebt = debt / days;
        double dailyBalance = (getBalance() - debt) / days;
        double annualInterest = dailyBalance * getAnnualInterestRate() - dailyDebt * debtInterestRate;
        cout << "The annual interest is $" << fixed << setprecision(2) << annualInterest << endl;
        return annualInterest;
    }
};

void saveAccount(Account* account) {
    ofstream fout(account->getAccountNumber() + ".txt");
    fout << fixed << setprecision(2);
    fout << account->getAccountNumber() << endl;
    fout << account->getBalance() << endl;
    fout << account->getAnnualInterestRate() << endl;
    fout.close();
}

Account* loadAccount(string accountNumber) {
    ifstream fin(accountNumber + ".txt");
    if (!fin.is_open()) {
        return nullptr;
    }
    string number;
    double balance;
    double annualInterestRate;
    fin >> number >> balance >> annualInterestRate;
    fin.close();
    Account* account = new Account(number, balance, annualInterestRate);
    return account;
}

void saveCreditAccount(CreditAccount* account) {
    ofstream fout(account->getAccountNumber() + ".txt");
    fout << fixed << setprecision(2);
    fout << account->getAccountNumber() << endl;
    fout << account->getBalance() << endl;
    fout << account->getAnnualInterestRate() << endl;
    fout << account->getCreditLimit() << endl;
    fout << account->getDebt() << endl;
    fout << account->getDebtInterestRate() << endl;
    fout.close();
}

CreditAccount* loadCreditAccount(string accountNumber) {
    ifstream fin(accountNumber + ".txt");
    if (!fin.is_open()) {
        return nullptr;
    }
    string number;
    double balance;
    double annualInterestRate;
    double creditLimit;
    double debt;
    double debtInterestRate;
    fin >> number >> balance >> annualInterestRate >> creditLimit >> debt >> debtInterestRate;
    fin.close();
    CreditAccount* account = new CreditAccount(number, balance, annualInterestRate, creditLimit, debt, debtInterestRate);
    return account;
}

int main() {
    Account* account1 = new Account("1234567890", 1000.00, 0.01);
    saveAccount(account1);
    Account* account2 = loadAccount("1234567890");
    cout << "Account " << account2->getAccountNumber() << " balance is $" << fixed << setprecision(2) << account2->getBalance() << endl;
    account2->deposit(500.00);
    saveAccount(account2);
    account2->withdraw(2000.00);
    account2->calculateInterest();

    CreditAccount* account3 = new CreditAccount("0987654321", 1000.00, 0.01, 2000.00, 500.00, 0.05);
    saveCreditAccount(account3);
    CreditAccount* account4 = loadCreditAccount("0987654321");
    cout << "Credit Account " << account4->getAccountNumber() << " balance is $" << fixed << setprecision(2) << account4->getBalance() << endl;
    account4->overdraft(1500.00);
    saveCreditAccount(account4);
    account4->repayment(1000.00);
    account4->calculateInterest();

    delete account1;
    delete account2;
    delete account3;
    delete account4;

    return 0;
}

在这个示例中，我们使用了文件来存储所有用户信息，每个账户信息存储在一个单独的文本文件中，文件名使用账号作为标识符。在程序启动时，我们可以创建账户对象并保存到文件中，也可以从文件中读取账户对象。在程序结束时，我们需要将所有账户对象保存到文件中。

对于账户类和信用卡账户类，我们分别实现了存款、取款、结算利息、透支和还款等方法，并且在每个方法中修改当前的余额并且将余额的变动输出。利息计算的实现也与要求相符，将一年中每天的余额累计起来再除以一年的总天数。