php隔行换色输出表格

<?php
    header("Content-type:text/html;charset=utf-8");
    $str='';
    $str.='<table border="1"  class="show_left" style="margin-left:50px; width:auto;">';
    $str.='<tr>';
        $str.='<td class="one" align="center">品类编号</td>';
        $str.='<td class="one" align="center">品类名称</td>';
        $str.='<td class="one" align="center">添加时间</td>';
        $str.='<td class="one" align="center">等　　级</td>';
        $str.='<td class="one" align="center">状　　态</td>';
        $str.='<td class="one" align="center">备　　注</td>';
    $str.='</tr>';
    ;$i<;$i++){
        ==){
            $str.='<tr style="background-color:pink;">';
            $str.='<td  align="center" class="one">1</td>';
            $str.='<td  align="center" class="one">sdasd</td>';
            $str.='<td  align="center" class="one">fdgs</td>';
            $str.='<td  align="center" class="one">dsfasdf</td>';
            $str.='<td  align="center" class="one">fgdsgs</td>';
            $str.='<td  align="center" class="one">ewrwrw</td>';
            $str.='</tr>';
        }else{
            $str.='<tr style="background-color:gray;">';
            $str.='<td  align="center" class="one">1</td>';
            $str.='<td  align="center" class="one">sdasd</td>';
            $str.='<td  align="center" class="one">fdgs</td>';
            $str.='<td  align="center" class="one">dsfasdf</td>';
            $str.='<td  align="center" class="one">fgdsgs</td>';
            $str.='<td  align="center" class="one">ewrwrw</td>';
            $str.='</tr>';
        }
    }
    $str.='</table>';
    echo $str;
?>