$code = $_GET["c"];

$db = new MySQLi("localhost","root","159357","renyuanxinxi");

$ainfo = "select * from info where code='{$code}'";

$binfo = $db->query($ainfo);

$cinfo = $binfo->fetch_row();

<form action="xiugaichuli.php" method="post">

    <div><input type="hidden" name="code" value="<?php echo $ainfo[0]; ?>" /></div>

    <div>姓名：<input type="text" name="name" value="<?php echo $ainfo[1]; ?>" /></div>

    <div>性别：                           //true   false判定

    <input type="radio" name="sex" value="1" <?php echo $ainfo[2]?"checked='checked'":"" ?> />男

    &nbsp;

    <input type="radio" name="sex" value="0" <?php echo $ainfo[2]?"":"checked='checked'" ?> />女

    </div>

    <div>民族：

    <select name="nation">

        <?php

        $sql = "select * from nation";

        $result = $db->query($sql);

        $attr = $result->fetch_all();

        foreach($attr as $v)               //下拉列表设默认

        {

            if($v[0]==$ainfo[3])

            {

                echo "<option selected='selected' value='{$v[0]}'>{$v[1]}</option>";

            }

            else

            {

                echo "<option value='{$v[0]}'>{$v[1]}</option>";

            }

        }

        ?>

    </select>

    </div>

    <div>生日：<input type="text" name="birthday" value="<?php echo $ainfo[4]; ?>" /></div>

    <div><input type="submit" value="修改" /></div>

</form>        

<?php

$code = $_POST["code"];                         //取值

$name = $_POST["name"];

$sex = $_POST["sex"];

$nation = $_POST["nation"];

$birthday = $_POST["birthday"];

$db = new MySQLi("localhost","root","159357","renyuanxinxi");

$sql = "update info set name='{$name}',sex={$sex},nation='{$nation}',birthday='{$birthday}' where code='{$code}'";//用修改语句 根据主键值 选择所要修改的列

$db->query($sql);                 //执行

header("location:main.php");