This is a calculator I made in 20 mins while getting bored in English. That is why (Pardon the pun......) I checked my spellings (syntax) over and over :)
Very good effort. You need to tell the user at the start what functions the calculator supports. Also, it should be able to handle decimals e.g. 12.5. You might like to make another version that uses functions to get input, do calculations etc. One last thought: how does the user exit from the program?