For the programs we write in Visual Basic, however, we will have to work a little harder to ensure that the data sent to the program is valid because we will need to include validation logic in our program code.

In a software project of any size, the task of determining what is and isn't valid data is usually undertaken long before any code is written, and is part of the requirements analysis phase.

validating textbox in vb net-36

Text) = 0 Then Exit Sub Else For i = 0 To Len (txt Telephone.

Text) - 1 If In Str (1, str Allowed Chars, txt Telephone.

The password fields are a good example of a situation where you can reduce the requirements for data validation by imposing such a limit.

Set the number of characters (since the maximum number cannot be exceeded in any case) .

Proceed as follows: Note that the last box requires the user to input the result of a simple sum (randomly generated) to prevent web robot programs from hijacking the form.

The popular term CAPTCHA (an approximate abbreviation of ) is often used to describe this kind of validation.

The same is true for the user's date of birth (DOB) and the CAPTCHA sum (which as you will see, can never exceed two digits) .

Dim str Allowed Chars As String = "0123456789 () - " If Len (txt Telephone.

is the process of ensuring, at least as far as is possible, that the data given to a program by a user or from a file (essentially, the program's input) is of the correct type and in the correct format.