Android Question String to Number

Hi guys.
I'm new to the forum and hope that I make no question that has been repeatedly answered.
I try to all examples in the forum but all examples ("1234") work with small numbers.
My Problem:
I have a number from a text box and wont add 100

Dim Str RC As String
Dim IntRC As Int
StrRC = "137215641588"
IntRC = StrRC + 100 'Result 2147483647

Dim StrRC As String
Dim IntRC As Double
StrRC = "137215641588"
IntRC = StrRC + 100 'Result 137215641688E11

Please help me.