Calculadora

   <h2>Calculadora</h2>
            <input type="text" class="form-control" id="num1" value="4">
            <input class="btn btn-info" type="button" id="sumar" value="+">
            <input class="btn btn-info" type="button" id="restar" value="-">
            <input class="btn btn-info" type="button" id="multiplicar" value="*">
            <input class="btn btn-info" type="button" id="dividir" value="/">
            <input type="text" class="form-control" id="num2" value="5">
            <h3>=</h3>
            <input type="text" class="form-control" id="res">

$(function () {
    $("#sumar").click(function () {
        var n1 = Number($('#num1').val());
        var n2 = Number($('#num2').val());
        $('#res').val(n1 + n2);
    });
    $("#restar").click(function () {
        var n1 = Number($('#num1').val());
        var n2 = Number($('#num2').val());
        $('#res').val(n1 - n2);
    });
    $("#multiplicar").click(function () {
        var n1 = Number($('#num1').val());
        var n2 = Number($('#num2').val());
        $('#res').val(n1 * n2);
    });
    $("#dividir").click(function () {
        var n1 = Number($('#num1').val());
        var n2 = Number($('#num2').val());
        $('#res').val(n1 / n2);
    });
});