How to: Search Within a String (Visual Basic)
The IndexOf method reports the location of the first character of the first occurrence of the substring. The index is 0-based, which means the first character of a string has an index of 0.
If IndexOf does not find the substring, it returns -1.
The IndexOf method is case-sensitive and uses the current culture.
For optimal error control, you might want to enclose the string search in the Try block of a Try...Catch...Finally Statement (Visual Basic) construction.