please help make this code workable in c# internal class client

$\{$

public string clientID;

public string firstName;

public string lastName;

public double purchaseAmount;

public client$($string ClientID, string firstName, string lastName, double purchaseAmount$)$

$\{$

this.clientID $=$ ClientID;

this.firstName $=$ firstName;

this.lastName $=$ lastName;

this.purchaseAmount $=$ purchaseAmount;

$\}$

class program

$\{$

static void Main$($string$[]$ args$)$

$\{$

int option $=0$;

while $($option $!=4)$

$\{$

Console.WriteLine$("$Main Menu: $")$;

Console.WriteLine$("1.$ Create new client"$)$;

Console.WriteLine$("2.$ Display a client"$)$;

Console.WriteLine$("3.$ Display all clients"$)$;

Console.WriteLine$("4.$ Exit"$)$;

Console.Write$("$select an option: $")$;

option $=$ int.Parse$($Console$.$ReadLine$())$;

switch $($option$)$

$\{$

case $1$:

CreateNewClient$()$;

break;

case $2$:

displayClientData$()$;

break;

case $3$:

displayAllClients$()$;

break;

case $4$:

Console.WriteLine$("$Exiting$...")$;

break;

default:

Console.WriteLine$("$Invalid option, please try again."$)$;

break;

$\}$

void createClient$()$

$\{$

string clientID, firstName, lastName;

double purchaseAmount;

Console.WriteLine$("$create a new client:"$)$;

Console.Write$("$Enter client ID $(3-$digit numerical string$)$: $")$;

clientID $=$ Console.ReadLine$()$;

Console.Write$("$Enter first name: $")$;

firstName $=$ Console.ReadLine$()$;

Console.Write$("$Enter last name: $")$;

lastName $=$ Console.ReadLine$()$;

Console.Write$("$eEnter purchase amount: $")$;

while $(!$double.TryParse$($Console$.$ReadLine$(),$ out purchaseAmount$))$

$\{$

Console.WriteLine$("$Invalid input, please try again."$)$;

Console.Write$("$Enter purchase amount: $")$;

$\}$

client newClient $=$ new client$($clientID$,$ firstName, lastName, purchaseAmount$)$;

Console.WriteLine$("$new client created:"$)$;

displayClientData$($newClient$)$;

Console.Write$("$creat another client? $($Y$/$N$)$: $")$;

string choice $=$ Console.ReadLine$()$;

if $($choice$.$Equals$("$Y$",$ StringComparison.OrdinalIgnoreCase$))$

$\{$

createClient$()$;

$\}$

$\}$

void displayClient$($client client$)$

$\{$

Console.Write$("$Enter client ID: $")$;

string clientID $=$ Console.ReadLine$()$;

client client$1=$ FindClient$($clientID$)$;

if $($client$1!=$ null$)$

$\{$

displayClient$($client$1)$;

$\}$

else

$\{$

Console.WriteLine$("$client not found."$)$;

$\}$

$\}$

$\}$

$\}$

$\}$

$\}$

$\}$