<?php


$comentarios = $_POST;

echo "<form method='post' action='#'>";

$nr_comentarios = count($_POST)-1;

for ($i = 0; $i < $nr_comentarios; $i++) {
    echo "<input type='text' name='$i' class='form-control' value='$comentarios[$i]'><br>";
};

if(isset($_POST['new'])){
    if($_POST['new'] != ''){
    echo "<input type='text' name='$nr_comentarios' class='form-control' value=".$comentarios['new']."><br>";
    }
}
    echo "<input type='text' name='new' class='form-control'><br>";
    echo "<button type='submit' class='btn btn-default'>Enviar</button>
</form>";