Why do you need such calculator? The Web calculator is already created, called JavaScript. :-)
Well, perhaps it needs some HTML to visualize it, present to a Web application user properly, process exceptions, etc.
Here is what you can get as a result:
My on-line calculator.
Real calculator should enable the user to introduce variables, create functions and even classes — all that JavaScript can do. Numerous computer simulations of old-days calculator with buttons, like Microsoft Windows calculator is something I call "civilization idiocy". Who need such things?
—SA