calc.js

var Calculator = (function(){
    var first = 0;
    var second = 0;
    var current_op = null;
    var result = null;
    function update_screen(digits) {
        $("#screen").text(digits);
    }
    function type_number(num) {
        if (current_op !== null) {
            if (second === null) {
                second = 0;
            }
            second = (second * 10) + num;
            update_screen(second);
        } else {
            // i.e. they hit =, then a number
            if (result === first) {
                result = null;
                first = 0;
            }
            first = (first * 10) + num;
            update_screen(first);
        }
    }
    function type_clear() {
        first = 0;
        second = result = current_op = null;
        update_screen(0);
    }
    function solve() {
        if (current_op === "+") {
            result = first + second;
        }
        else if (current_op === "-") {
            result = first - second;
        }
        else if (current_op === "*") {
            result = first * second;
        }
        else if (current_op === "/") {
            result = first / second;
        } else {
            return;
        }
        current_op = null;
        first = result;
        second = null;
    }
    function type_operation(operation) {
        if (current_op !== null) {
            solve();
        }
        if (operation !== "=") {
            current_op = operation;
        }
        update_screen(first);
    }
    return {"clear":type_clear,"number":type_number,"operation":type_operation};
})();