title: Validating WinForms TextBox (in C#)
body: <p>In TextBox_Leave event i need to check whether numbers entered in textbox is in serial number or not.If it is not in order then i need to display a message as "number" is missing </p>
  
  <p>For example :</p>
  
  <p>In textbox i have entered 3 and click tab :
  I need to display message as 
  "Number is not in order , number "1" and "2"  is missing "</p>