How to VB.NET String.IndexOf()

The IndexOf method in String Class returns the index of the first occurrence of the specified substring.

System.String.IndexOf(String str) As Integer
  1. str - The parameter string to check its occurrences.
  1. Integer - If the parameter String occurred as a substring in the specified String

It returns position of the first character of the substring .

If it does not occur as a substring, -1 is returned.

Exceptions: System.ArgumentNullException: If the Argument is null.

For ex:

"This is a test".IndexOf("Test") returns 10

"This is a test".IndexOf("vb") returns -1

Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles Button1.Click
        Dim str As String
        str = "VB.NET TOP 10 BOOKS"
    End Sub
End Class

When you execute this program you will get the number 14 in the message box. That means the substring "BOOKS" occurred and start in the position 14.