VB.NET Language in a Nutshell, Second Edition

Name

Asc, AscW Functions

Class

Microsoft.VisualBasic.Strings

Syntax

Asc(string)
AscW(str)

string, str (required; String or Char)

Any expression that evaluates to a nonempty string

Return Value

An Integer that represents the character code of the first character of the string. The range for the returned value is 0 - 255 on nonDBCS systems, and -32768 to 32767 on DBCS systems.

Description

Returns an Integer representing the character code for the first character of the string passed to it. All other characters in the string are ignored

Rules at a Glance

• The string expression passed to the function must contain at least one character or a runtime error is generated.

• Only the first character of the string is evaluated by Asc or AscW.

Example

Dim sChars As String
Dim iCharCode As Integer
    
sChars = TextBox1.Text
If Len(sChars) > 0 Then
   iCharCode = Asc(sChars)
   If iCharCode >= 97 And iChar <= 122 Then
      MsgBox "The first character must be uppercase"
   End If
End If

Programming Tips and Gotchas

• Check that the string you are passing to the function contains at least one character using the Len function, as the following example shows:

  If Len(sMyString) > 0 Then
      iCharCode = Asc(sMyString)
  Else
      MsgBox("Cannot process a zero-length string")
  End If

• Use Asc within your data-validation routines to determine such conditions as whether the first character is upper- or lowercase and whether it is alphabetic or numeric, as the following example demonstrates:

  Private Sub Button1_Click(ByVal sender As System.Object, ...