$(document).ready(function () {
    var result = 0;
    var prevEntry = 0;
    var operation = null;
    var currentEntry = '0';
    updateScreen(result);

    $(".button").on("click", function () {
        var currentvalue = $(this).html()
        console.log(currentvalue);
        if (isNumber(currentvalue)) {
            if (currentEntry === '0') currentEntry = currentvalue;
            else currentEntry = currentEntry + currentvalue;
            result = currentEntry;
            updateScreen(result);
        }
        else if (isOperator(currentvalue)) {
            prevEntry = parseFloat(currentEntry);
            operation = currentvalue;
            console.log(operation);
            currentEntry = '';
            result = currentEntry;
            updateScreen(result);

        }
        else if (currentvalue === '=') {
            currentEntry = operate(prevEntry, currentEntry, operation);
            operation = null;
            updateScreen(currentEntry);
        }
    });




    function isNumber(number) {
        return !isNaN(number)
    }

    isOperator = function (value) {
        return value === '/' || value === '*' || value === '+' || value === '-';
    };

    operate = function (a, b, operation) {
        a = parseFloat(a);
        b = parseFloat(b);
        console.log(a, b, operation);
        if (operation === '+') return a + b;
        if (operation === '-') return a - b;
        if (operation === '*') return a * b;
        if (operation === '/') return a / b;
    }


    function updateScreen(displayValue) {
        var displayValue = displayValue.toString();
        $('.screen').val(displayValue.substring(0, 10));

    }
});