Ah, well what you have to do is use the to_s method which happens to be a method of the Integer class. The Help File defines the method as "Converts an integer to a base-10 string expression." So to keep it plain and simple, this "to_s" method converts your integer into a string, which seems to be what you're looking for.
So in effect, you would change this:
string = "Graphics\\Characters\\" + number + ".png"
string = "Graphics\\Characters\\" + number.to_s + ".png"
Then instead of looking for the actual Integer 1, it would look for the string "1". Hope this helps