InStr Function in VB.NET

The Instr and InStrRev functions are still supported in .NET, but they are not the official way to handle strings.

The IndexOf and LastIndexOf functions are available for every string in .NET.  So, for example:
Dim i as Integer

'Use the "IndexOf" method with a regular string.
i = "My String".IndexOf("String")

'Use the "IndexOf" method with a string variable.
Dim str as String = "This is another string"
i = str.IndexOf("string")

'Use the "IndexOf" method with a TextBox, because the "Text" property is a String.
Dim tb As New TextBox
tb.Text = "my string"
i = tb.Text.IndexOf("string")

'Here is a LastIndexOf example for you:
Dim strFilePath As String = "C:\Temp\MyFile.txt"
Dim i As Integer
i = strFilePath.LastIndexOf("\")
     ' i now equals the integer 7:  the exact position of the last "\" (see notes below).

** Only 2 points to be aware of as you start using IndexOf and LastIndexOf:
1.  If no match is found, then a -1 is returned, not a 0 as with the Instr and InstrRev functions.
          'Here, a -1 will be returned, because the question mark is not found.
          i = "My String".IndexOf("?")

2.  Strings are zero (0) based in .NET.
          'So for example, the integer "3" will be returned,
          '      because the first character in the string "M" is position 0.
          i = "My String".IndexOf("String")

One final note:
'If you want to search for an exact match, then use the default,
i = "My String".IndexOf("String")

'However, if you want to search for a string, but you want to ignore the case
'such as UPPER CASE, Mixed Case, and lower case, then make sure you use the following:
i = "My String".IndexOf("string", StringComparison.CurrentCultureIgnoreCase)

So, in summary:
-  If you used the Instr method in VB6, use the IndexOf method in .NET.
-  If you used the InstrRev method in VB6, use the LastIndexOf method in .NET.