Calculator App

I had real trouble dealing with large numbers. Converting to exponential notation causes loosing precision, and I haven't found easy solution. I came across BigInt type, but what to do with decimal numbers? Solution, or reading recommendation are welcome. Another trouble I had with limiting input-how long numbers the app should receive? And, should input be limited? My decision was to limit it to 15, made mostly by design, previously mentioned problem, and task itself-this is supposed to be very basic calculator, performing basic arithmetic operation. Should it be limited at all, and, if not, how to deal with very, very large numbers, in calculation, but also in presentation? Should overflow be allowed, or the number should break in multiple lines? I'm not sure about either, and shrinking text can't go endlessly... Is there any convention on this? Or any advice?