This means that as a programmer, you have the power to supply the exact pattern for the input you desire in any text input field. Again, certain special characters are obviously not allowed.

They make use of a pattern matching system to match the input with a certain pattern of data.

Also, the more tests you are performing, the slower your app might become. For more information regarding Regular Expressions, you are welcome to look at these two MSDN articles: Because it is always easy to learn by doing things practically, you will be creating an app that makes use of Regular Expressions to determine valid input. NET application and design the form to resemble Figure 1. Obviously this only works for the formatting of the email.Sometimes people are just trying to be funny, or they are literally trying to break your program. If the data is indeed only alphabetic letters (no symbols, no numbers or any other punctuation characters) the test succeeds and stores True inside the Name Valid variable. This is because it becomes more legible than just a normal set of numbers. You could say that a program's testers are supposed to do this; yes, they should - nobody else should. If not, if there is even just one unallowed character that is not supposed to be there, the Match method will return False. Instead of you having to loop through each character to determine what that character is, you simply need the correct Regular Expression pattern. Clear() Surname Valid = False Else Surname Valid = True End If End Sub It is basically the exact same code for the Name box, but I just included the capability to comprehend a space character as well. People expect to enter a phone number in a format similar to this: ###-###-####. The National Electronic Identity Card (e-ID card) is a chip based card with multiple functions.The card is a token given upon successful enrolment or registration into the National Identity System.Figure 1 - These objects will determine if all our data is valid or not. Clear() 'Clear Text Box Name Valid = False 'Boolean = False Else Name Valid = True 'Everything Fine End If End Sub Easy one to start with. Focus() 'Set Focus To Text Box End If End Sub Private Sub txt Email_Lost Focus(sender As Object, e As System. Lost Focus Validate Email() 'Check Email Validity End Sub The expression may look horrible to the layman's eye, but look closer. To check if the user has entered an email that actually exists, you will have to find a different way such as to send a of some sorts.Based on each of these variables' values, we will know if the data is correct or not. The Leave event fires when the control loses focus. As you can see, Regular Expressions are a vital tool to have at your disposal, so become good friends with them.