Create a C# GUI prototype for an online bank. The program requires an account number and pin number to login. Once logged in, the user can deposit or withdraw money. When the user is done, they can log out of the system. There can only be one user logged in at a time. The program should have at least 5 accounts.

Methods Login() accepts an account number and pin number as strings. If valid, logs the user in, displays a welcome message, and displays their balance. If invalid, logs out the previous user and displays an error message. Logout() logs out the active user. MakeDeposit() accepts a deposit amount as a decimal and displays the user's updated balance. MakeWithdrawal() accepts a withdrawal amount as a decimal and displays the user's updated balance.