C# Example 1

using System;
using System.Collections.Generic;

// Kaizer here. I created a banking system, which allows you to create your own account, withdraw money, input account numbers, initial balance, and so on and so forth.

// class to represent a bank account
class Account
{
    private string accountNumber;
    private string accountHolder;
    private double balance;

    // constructor for initializing account details
    public Account(string accNumber, string accHolder, double initialBalance)
    {
        accountNumber = accNumber;
        accountHolder = accHolder;
        balance = initialBalance;
    }

    // function to find an already existing account number
    public string GetAccountNumber()
    {
        return accountNumber;
    }

    // function to deposit money into the account
    public void Deposit(double amount)
    {
        if (amount > 0)
        {
            balance += amount;
            Console.WriteLine($"Deposited: {amount}");
        }
        else
        {
            Console.WriteLine("Invalid deposit amount.");
        }
    }

    // function to withdraw money from the account
    public void Withdraw(double amount)
    {
        if (amount > 0 && amount <= balance)
        {
            balance -= amount;
            Console.WriteLine($"Withdrew: {amount}");
        }
        else
        {
            Console.WriteLine("Invalid withdrawal amount or insufficient funds.");
        }
    }

    // function to check the account balance
    public double GetBalance()
    {
        return balance;
    }

    // function to display account details
    public void Display()
    {
        Console.WriteLine($"Account Number: {accountNumber}");
        Console.WriteLine($"Account Holder: {accountHolder}");
        Console.WriteLine($"Balance: {balance}");
    }
}

// public Class to manage multiple accounts
class Bank
{
    private List<Account> accounts = new List<Account>();

    // function to create a new account
    public void CreateAccount(string accNumber, string accHolder, double initialBalance)
    {
        accounts.Add(new Account(accNumber, accHolder, initialBalance));
        Console.WriteLine("Account created successfully.");
    }

    // function to find an account by account number
    public Account FindAccount(string accNumber)
    {
        return accounts.Find(account => account.GetAccountNumber() == accNumber);
    }

    // function to display all accounts
    public void DisplayAllAccounts()
    {
        foreach (var account in accounts)
        {
            account.Display();
            Console.WriteLine("-------------------");
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        Bank bank = new Bank();
        int choice;
        string accNumber, accHolder;
        double amount;

        do
        {
            Console.WriteLine("1. Create Account");
            Console.WriteLine("2. Deposit");
            Console.WriteLine("3. Withdraw");
            Console.WriteLine("4. Check Balance");
            Console.WriteLine("5. Display All Accounts");
            Console.WriteLine("6. Exit");
            Console.Write("Enter your choice: ");
            choice = int.Parse(Console.ReadLine());

            switch (choice)
            {
                case 1:
                    Console.Write("Enter account number: ");
                    accNumber = Console.ReadLine();
                    Console.Write("Enter account holder name: ");
                    accHolder = Console.ReadLine();
                    Console.Write("Enter initial balance: ");
                    amount = double.Parse(Console.ReadLine());
                    bank.CreateAccount(accNumber, accHolder, amount);
                    break;
                case 2:
                    Console.Write("Enter account number: ");
                    accNumber = Console.ReadLine();
                    Account account = bank.FindAccount(accNumber);
                    if (account != null)
                    {
                        Console.Write("Enter amount to deposit: ");
                        amount = double.Parse(Console.ReadLine());
                        account.Deposit(amount);
                    }
                    else
                    {
                        Console.WriteLine("Account not found.");
                    }
                    break;
                case 3:
                    Console.Write("Enter account number: ");
                    accNumber = Console.ReadLine();
                    account = bank.FindAccount(accNumber);
                    if (account != null)
                    {
                        Console.Write("Enter amount to withdraw: ");
                        amount = double.Parse(Console.ReadLine());
                        account.Withdraw(amount);
                    }
                    else
                    {
                        Console.WriteLine("Account not found.");
                    }
                    break;
                case 4:
                    Console.Write("Enter account number: ");
                    accNumber = Console.ReadLine();
                    account = bank.FindAccount(accNumber);
                    if (account != null)
                    {
                        Console.WriteLine($"Balance: {account.GetBalance()}");
                    }
                    else
                    {
                        Console.WriteLine("Account not found.");
                    }
                    break;
                case 5:
                    bank.DisplayAllAccounts();
                    break;
                case 6:
                    Console.WriteLine("Exiting...");
                    break;
                default:
                    Console.WriteLine("Invalid choice. Please try again.");
                    break;
            }
        } while (choice != 6);
    }
}