即使输入为假，if 语句也始终显示为真答案

【问题标题】：if statement always display true even the input is false即使输入为假，if 语句也始终显示为真
【发布时间】：2013-09-26 20:14:23
【问题描述】：

<?php

    include("connection2.php");     

    if(!empty($_POST['lrn'])  && !empty($_POST['password'])){

        $lrn = $_POST['lrn'];
        $pass = $_POST['password'];
        $check = "SELECT * from studentinf where LRN = '".$lrn."'";
        $qry = mysql_query($check);
        $num_rows = mysql_num_rows($qry); 
        $check2 = "SELECT * from studentinf where Password = '".$pass."'";
        $qry2 = mysql_query($check2);
        $num_rows2 = mysql_num_rows($qry2); 

        if($num_rows > 0){
            echo "<center>LRN is valid</center> ";
        }

        else 
            echo "<font color='#FF0000'><center>Your LRN is Invalid. <br>Please Contact your Web   Administrator for your LRN.</center></font>";


        if($num_rows2 != "")
        {
            echo "account already registered";            
        }

        else if ($num_rows2 == "")
        {
            echo "account not yet registered";
            $query = "UPDATE studentinf SET Password = '$pass' where LRN = '$lrn'";
            mysql_query($query);

            echo "Thank You for Registration.";
            echo '<br><a href="studentlogin.php">Click Here</a> to login your account.';
        }
    }
 ?>

【问题讨论】：

heremycodefixitformeplzthanks。尝试减少您的问题，并至少解释导致错误的行。
里面有 4 个 if 语句，你遇到了哪些问题？
嗯.. 至少它是可破解的。
看到你的代码我看到密码不是散列的坏主意，而且 ---------- >Please, don't use mysql_* functions in new code。它们不再维护and are officially deprecated。看到red box？改为了解prepared statements，并使用PDO 或MySQLi - this article 将帮助您决定哪个。如果你选择 PDO，here is a good tutorial.
^ 你们太棒了。

标签： php registration

【解决方案1】：

如果我猜对了您所说的 if 语句，请尝试替换：

if($num_rows2 != "")
{
  echo "account already registered";
}
else
if ($num_rows2 == "")
{
  // ...
}

与：

if ($num_rows2 > 0)
{
  echo "account already registered";
}
else
{
  // ...
}

$num_rows2 是数字；将其与数字而非字符串进行比较。

【讨论】：