检查字符串中的第一个字符-电话号码

Question

Could you please help me with the validation of a phone number? I have already validated it to have 11 characters, but I don't know how to make a condition for the first character to be 0.

Thank you!

Here is the code:

Do
        tel_no(n) = InputBox("Enter the telephone number")
        If Len(tel_no(n)) < 11 Or Len(tel_no(n)) > 11 Then
            MsgBox("The telephone number should have 11  digits and should start with 0")
        End If

Loop Until Len(tel_no(n)) = 11

Answer 1

You can try to validate it this way :

.......
tel_no(n) = InputBox("Enter the telephone number")
If (tel_no(n).Length <> 11) Or (tel_no(n)(0) <> "0") Then
    MsgBox("The telephone number should have 11  digits and should start with 0")
End If
.......

That will make sure that tel_no(n) has length exactly 11, and has character in index 0 (the first character) equals zero ( 0 ).

Answer 2

Try this:

Dim conditionMet As Boolean = False

Do
    Dim phoneNumber As String = InputBox("Enter the telephone number")

    conditionMet = phoneNumber.Length = 11 And phoneNumber.StartsWith("0")

    If Not conditionMet Then
        MsgBox("The telephone number should have 11 digits and should start with 0")
    Else
        tel_no(n) = phoneNumber
    End If

Loop Until conditionMet

I should mention though that your user would have a much better UI experience if you showed him a MaskedTextBox instead.