Answer 1

As far as I know(which isn't much but still), almost--if not all programming language like java and python are capable of programming a calculator.
not the case for backend language like sql though,i think.

a c++example:
cout<<"do you want addition(1),blahblahblah."<<endl;
cin>>choice;
cout<<"Enter two numbers"<<endl;
cin>>a>>b;
switch(choice){
case 1:
cout<<a+b;
break;
}

and so on.
Hope this helps.