In that case, the validation is performed as users work in the browser.
Well, sometimes a good structured and thought out If statement can suffice, but it can become quite long and cumbersome in the future. By using Regular Expressions this way, you can reduce the chances of getting errors at erratic times. This sub checks the email's format and if it thinks that it matches, it returns True and vice versa.
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.
Even if users correctly enter an integer, for example, you might need to make sure that the value falls within a certain range.
Important Validating user input is also important for security.
Client-based validation can also reduce the number of times that the user has to submit the form to correct multiple errors.