VS 2010 - How To Get Part Of String

Public Class Form1
Private Sub but_convert_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles but_convert.Click
Dim input_string As String
Dim output_string As String
Dim fkey_string As String
[Code] .....

So, the big thing is that I want to use that code to transform this:
if(strcmp(cmd, "/quitjob", true) == 0) {
if(IsPlayerConnected(playerid)) {
if(GetPVarInt(playerid,"job") > 0) {
[Code] .....
The problem is that I get an empty text box when I click the button.