I made a sample application.

Author: oguzhanKomcu

Custom_Functions/AtmApp2.cs

@@ -21,6 +21,44 @@ public AtmApp2()
  Dictionary<string,string> usersFullName = new Dictionary<string, string>();
  List<double> usebalance = new List<double>();
 
+
+ bool numbercontrol(string text)
+ {
+
+
+ char[] control = text.ToLower().ToCharArray();
+ bool result = false;
+
+ foreach (char item in text)
+ {
+ switch (item)
+ {
+ case '1':
+ case '2':
+ case '3':
+ case '4':
+ case '5':
+ case '6':
+ case '7':
+ case '8':
+ case '9':
+ case '0':
+ result = true;
+ break;
+
+ default:
+ break;
+
+
+ }
+
+ }
+
+ return result;
+
+ }
+
+
  bool SignUpFullName( string firstname, string lastname)
  {
  if (firstname == "" && lastname == "")
@@ -45,14 +83,14 @@ bool SignUp(string userId, string password)
  if (userId != "" && userId.Length == 11 )
  {
 
- if (password != "" && password.Length > 5 )
+ if (password != "" && password.Length > 5 && numbercontrol(password) == true)
  {
  users.Add(userId, password);
  return true;
  }
  else
  {
- MessageBox.Show("You entered the wrong password or ID !!");
+ MessageBox.Show("You entered the wrong password or ID . Your password must have a number .!!");
  return false;
  }
 

Custom_Functions/Program.cs

@@ -11,7 +11,7 @@ static void Main()
  // To customize application configuration such as set high DPI settings or default font,
  // see https://aka.ms/applicationconfiguration.
  ApplicationConfiguration.Initialize();
- Application.Run(new BusTicketApp());
+ Application.Run(new AtmApp2());
  }
  }
 }