How to remove file extension using C#?
If you can, just use Path.GetFileNameWithoutExtension


  Returns the file name of the specified path string without the extension.


Path.GetFileNameWithoutExtension("asdasdasd.asdas.adas.asdasdasdasd.edasdasd");


With one line of code you can get the same result.

If you want to create one by yourself, why not just use this?

int index = a.LastIndexOf('.');
b = index == -1 ? a : a.Substring(0, index);


P.S Special thanks to @Anthony and @CompuChip to point me out some mistake i done, bad day maybe.

You take everything which comes from 0 (the start) to the last dot which means the start of the extension