How to convert a string to integer

Dim strValue as string
Dim valString as int

strValue = "100"
valString = strValue

If IsNumber(strValue) = True Then
    valString = strValue
Else
    Msgbox ( "the string is not a valid integer" , "error" )
End If

Sub CStr(o As Object) As String
 Return "" & o
End Sub

Sub CInt(o As Object) As Int
  Return Floor(o)
End Sub

Sub CLng(o As Object) As Long
  Return Floor(o)
End Sub

Dim strValue As String
Dim Result As Float
strValue = "100"
Result=Sqrt(strValue)
Msgbox("The square root of " & strValue & " is " &  Result,"")

   Dim Waiting_Time As EditText
   Dim Waiting_Time_Int As Int
   Dim tmpString As String
----------------------------
tmpString = Waiting_Time.Text
Waiting_Time_Int = tmpString + 1
tmpString = Waiting_Time_Int
Waiting_Time.Text = tmpString

java.lang.NumberFormatException: Invalid double: ""
Installing file.
PackageAdded: package:ce3.arsham.CE3RVCtrl
** Activity (main) Create, isFirst = true **
** Activity (main) Resume **
main_tmr1_tick (B4A line: 195)
Waiting_Time_Int = tmpString + 1
java.lang.NumberFormatException: Invalid double: ""
   at java.lang.StringToReal.invalidReal(StringToReal.java:63)
   at java.lang.StringToReal.parseDouble(StringToReal.java:248)
   at java.lang.Double.parseDouble(Double.java:295)
   at ce3.arsham.CE3RVCtrl.main._tmr1_tick(main.java:789)
   at java.lang.reflect.Method.invokeNative(Native Method)
   at java.lang.reflect.Method.invoke(Method.java:511)
   at anywheresoftware.b4a.BA.raiseEvent2(BA.java:169)
   at anywheresoftware.b4a.objects.Timer$TickTack.run(Timer.java:105)
   at android.os.Handler.handleCallback(Handler.java:725)
   at android.os.Handler.dispatchMessage(Handler.java:92)
   at android.os.Looper.loop(Looper.java:137)
   at android.app.ActivityThread.main(ActivityThread.java:5039)
   at java.lang.reflect.Method.invokeNative(Native Method)
   at java.lang.reflect.Method.invoke(Method.java:511)
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
   at dalvik.system.NativeStart.main(Native Method)

Waiting_Time.Text=Waiting_Time.Text+1

If IsNumber(Waiting_Time.Text) then
    Waiting_Time.Text=Waiting_Time.Text+1
Else
    Log(Waiting_Time.Text &" is not a number")
End If