php中的未定义变量（错误）[重复]

undefined variables(name, email, adm,add) on line 16 ....error is coming.....kindly help me to remove error here is my code

<?php

$con = mysqli_connect('localhost','root','');
if(!$con) { 
    echo 'not connected to database';
}
if(!mysqli_select_db($con,'student')) {
    echo 'database not selected';
}
if (isset($_POST['name'])){$name = $_POST['name'];}
if (isset($_POST['email'])){$email= $_POST['email'];}
if (isset($_POST['address'])){$add = $_POST['address'];}
if (isset($_POST['admission'])){$adm = $_POST['admission'];}

/*line:16*/                                                                        
$sql = "INSERT INTO student_record (name,email,address,joining_date) VALUES('$name','$email','$add','$adm')";
if ( !mysqli_query($con,$sql)) {
    echo 'not inserted';
} else {
    echo'inserted';
}

?>

</div>

This is due to you have not initialize your variable before the if conditions . if POST data not found then all 4 variables not set then error come. Plz try this

if($_POST){
    $con = mysqli_connect('localhost','root','');
    if(!$con)
    { 
        echo 'not connected to database';
    }
    if(!mysqli_select_db($con,'student'))
    {
        echo 'database not selected';
    }

    $error  =   true;
    $errorMessage   =   '';
    if (empty($_POST['name']) || empty($_POST['email']) || empty($_POST['address']) || empty($_POST['admission'])){
        $error  =   false;
        if(empty($_POST['name'])){
            $errorMessage   =   'Please enter name <br/>';
        }
        if(empty($_POST['email'])){
            $errorMessage   .=  'Please enter email <br/>';
        }
        if(empty($_POST['address'])){
            $errorMessage   .=  'Please enter address <br/>';
        }
        if(empty($_POST['admission'])){
            $errorMessage   .=  'Please enter admission <br/>';
        }
    }
    if($error){
        $name   = mysql_real_escape_string($_POST['name']);
        $email  = mysql_real_escape_string($_POST['email']);
        $add    = mysql_real_escape_string($_POST['address']);
        $adm    = mysql_real_escape_string($_POST['admission']);

        /*line:16*/                                                                        
        $sql = "INSERT INTO student_record (name,email,address,joining_date) VALUES('$name','$email','$add','$adm')";
        if ( !mysqli_query($con,$sql))
        {
            echo 'not inserted';
        }else{
            echo'inserted';
        }
    }else{
        echo $errorMessage;
    }
}

I think you are not getting any post data. Just add a if condition before the execution

if($_POST){  /*Do stuff check for the post['name'] run your SQL query */

as the post is not defined your POST['name'] is not set and it does not go the if block and remains not set.