创建银行账户类SavingAccount，用静态成员变量存储年利率，用私有成员变量存储存款余额。提供计算年利息的方法和计算月利息（年利息/12）的方法。在主函数中建立SavingAccount的对象saver，从控制台输入存款额度和年利率，输出年利息和月利息。保留两位小数

#include<iostream>
#include<iomanip>
using namespace std;

class SavingAccount{
private:
    static double annualInterestRate;
    double balance;
public:
    SavingAccount(double b){
        balance = b;
    }
    void calculateAnnualInterest(){
        double interest = balance * annualInterestRate;
        cout<<fixed<<setprecision(2)<<"Annual interest: "<<interest<<endl;
    }
    void calculateMonthlyInterest(){
        double interest = balance * annualInterestRate / 12;
        cout<<fixed<<setprecision(2)<<"Monthly interest: "<<interest<<endl;
    }
    static void modifyAnnualInterestRate(double rate){
        annualInterestRate = rate;
    }
};

double SavingAccount::annualInterestRate = 0.0;

int main(){
    double balance, rate;
    cout<<"Input balance: ";
    cin>>balance;
    cout<<"Input annual interest rate: ";
    cin>>rate;
    SavingAccount saver(balance);
    SavingAccount::modifyAnnualInterestRate(rate);
    saver.calculateAnnualInterest();
    saver.calculateMonthlyInterest();
    return 0;
}

输出样例：

Input balance: 1000
Input annual interest rate: 0.05
Annual interest: 50.00
Monthly interest: 4.17