Please tell me what's wrong with this calculator it is showing" no output " instead of a result

Question

Actually there is no error I can find but something else is being missed
https://code.sololearn.com/cgiU5gZ8xij3/?ref=app

Answer 1

compiling error !!

Answer 2

Prabhat Singh actually i corrected the code so it will work now
so please enjoy the code now..