[Dilettante_Pro]

Второе задание без явного цикла

<div class="p">5</div>
<div class="p">3</div>
<div class="p">1</div>
<div class="p">4</div>
<button class="btn">Sum</button>
<input type="text">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>

<script>
var num = $('.p'),
     btn = $('.btn'),
     inp = $('input');

    btn.on({
        'click': sum
    });

    function sum() {
        var arr = [];
        num.html(function(){ arr.push(+this.innerHTML)});
        inp.val(arr.sort(srt));
    }
    function srt(a, b) {
        if (a > b) {
            return 1;
        }
        if (a < b) {
            return -1;
        }
        if (a == b) {
            return 0;
        }
    }
</script>