如何简化if-else语句？

我完成了-非常菜鸟的创建，因为我仍然是菜鸟:(-充当银行帐户的程序。

我有main.cpp，Account.cpp，Account.h。

在main.cpp我有：

#include <iostream>
#include <string>
#include "Account.h"

int main()
{   
    Account Luigis;
    Luigis.set_name("Luigi's Account");
    Luigis.set_balance(0);
    std::string letter;
   
do  {
    std::cout << "Your current balance is: " << Luigis.get_balance() << std::endl;
    std::cout << "What would you like, to deposit, to withdraw or to exit?" << std::endl;
    std::cout << "(D for 'Deposit, W for 'Withdraw' and Q for 'Exit') D/W/Q ";
    std::cin >> letter;
    if(letter == "d" || letter == "D") {
        std::cout << "How much would you like to deposit?: ";
        double amountDeposit{};
        std::cin >> amountDeposit;
        Luigis.deposit(amountDeposit);
    }
        else if(letter == "w" || letter == "W") {
            std::cout << "How much would you like to withdraw?: ";
            double amountWithdraw;
            std::cin >> amountWithdraw;
            Luigis.withdraw(amountWithdraw);
        }
            else if(letter == "q" || letter == "Q") {
                std::cout << "Goodbye!" << std::endl;
            }
                else 
                std::cout << "Invalid selection, please try again with: D for Deposit, W for Withdraw, Q for Exist" << std::endl;
                
    
    } while (letter != "q" && letter != "Q");
    
    return 0;
}

在Account.cpp我有：

#include "Account.h"
#include <string>
#include <iostream>
//IMPLEMENTATION or DEFINITION

bool Account::deposit(double amount) {
    //money you're doing to deposit
    balance = balance + amount;
    }

bool Account::withdraw(double amount) {
        //if you can withdraw
        if(balance-amount >= 0) {
             balance = balance - amount;
             return true;
            } else {
                std::cout << "You cannot withdraw the specified amount - balance is too low and it would result in " << balance - amount << " funds!" << std::endl;
                return false;
                }
        }
    
void Account::set_name(std::string name) {
        this->name = name;
        }

std::string Account::get_name(){
        return name;
        }

void Account::set_balance(double balance) {
        this->balance = balance;
    }

double Account::get_balance() {
        return balance;
    }

而且Account.h我有：

#ifndef _ACCOUNT_H_
#define _ACCOUNT_H_
#include <string>
//SPECIFICATION or DECLARATION


class Account
{
private:
    //attributes
    std::string name;
    double balance;
public:
    //methods
    bool deposit(double amount);
    bool withdraw(double amount);
    void set_name(std::string name);
    std::string get_name();
    void set_balance(double balance);
    double get_balance();
};

#endif // _ACCOUNT_H_

我的问题是：既然我“知道”如何使用函数，现在如何简化if-else语句main.cpp？我的朋友说，我应该能够使用函数并使事情更抽象，以避免编写所有ifandelse语句。

基本上，我将OOP与过程编程混合在一起，这违背了目的。