Taking a string, converting it to an integer to call a method expecting an integer is one thing: but you can't then add strigns to it and expect it to remain an integer: what should I do with this?
%17% / 42
Mathematically, it's garbage - and that's what you are trying to pass to your method.
Either pass the integer value without adding strings to it, or write an overload fro your method which takes a string instead.