给id拼接变量，给nth-child()拼接变量

<div class="daic">
    <p class="reward"></p>
    <p class="reward"></p>
    <p class="reward"></p>
    <p class="reward"></p>
    <p class="reward"></p>
</div>

<p class="data"></p>

var num = 1;
$('<p id="data' + num + '"></p>').appendTo('body');

获取变量id的属性id

console.log($('#data' + num).attr('id'));

给每个reward赋值id为rewardi

for(var i=0;i<6;i++) {
    $('.daic .reward:nth-child(' + i + ')').attr('id','reward'+(i));
}