why i get an default output 0 after the invalid inputs?

Question

My requirement is to set two values in an html form and pass those values into an PHP file where i will check wither these value is set or not set.If any one or two of the field is blank than it will show invalid input. And if the values are set (including 0) than it will do some action like as adding operation.But the problem is that if i set 0 it takes the value as empty value than shows invalid and also shows 0 after the invalid input. is this because add method is called.any explanation ? please anyone help me to understand it clearly and also release me from the confusion of 0 and empty check.

My code is here,

HTML:

<input type="number" name="num1"">
<input type="number" name="num2">
<input type="submit" name="add" value="+">

PHP:

<?php
class calculator_oop
{
    public $num1;
    public $num2;
    public $result;
   public function __construct($number1,$number2){
       if( ((empty($number1) || empty($number2))))  {
           echo "Invalid inputs ";
       }
       else{
           $this->num1 = $number1;
           $this->num2 = $number2;
       }
   }
   public function add(){
       return $this->result = $this->num1 + $this->num2;
   }
}
$ob = new calculator_oop($_POST['num1'],$_POST['num2']);
if($_POST['add'] =='+' ){
    echo $ob-> add();
}

When I keep the field blank, I just wanna know why 0 appears after invalid input when I let them blank.

output: Invalid input 0

please add your codes as text format and delete the images ! — Ivan Barayev, Jan 01 '17 at 20:49
you should probably post the html form for this also. If not, then see the answer you've been given below. — Funk Forty Niner, Jan 01 '17 at 21:06
here i have given the form code. but when i remove the if condition after the object i get only invalid input .but when the add method is called and the fields are blank than the 0 appears. why this happen ? — Ariful Haque Anna, Jan 01 '17 at 21:17
@ArifulHaqueAnna I have explained it in my answer below http://stackoverflow.com/a/41419176/1415724 — Funk Forty Niner, Jan 01 '17 at 21:27

score 0 · Answer 1 · answered Jan 01 '17 at 20:59

In PHP, the following things are considered to be empty:

"" (an empty string)
0 (0 as an integer)
0.0 (0 as a float)
"0" (0 as a string)
NULL
FALSE
array() (an empty array)
$var; (a variable declared, but without a value)

if you want to test zero use :

$var == 0 or $var == "0"

you have to understand this :

<?php
$var = 0;

// Evaluates to true because $var is empty
if (empty($var)) {
    echo '$var is either 0, empty, or not set at all';
}

// Evaluates as true because $var is set
if (isset($var)) {
    echo '$var is set even though it is empty';
}
?>

Please read : http://php.net/manual/en/function.empty.php

score 0 · Accepted Answer · edited May 23 '17 at 11:53

What's happening here is, 0 is considered as being empty (consult the reference on this below), but you've also (or may have) entered 0 in the input(s), to which in the eye of PHP and at the time of execution, is considered as being "not empty" at the same time, since the input(s) was/were not left "empty" which is sort of fighting for precedence/contradicting itself at the same time.

What you want/need to check is to see if it/they is/are numeric or not by using is_numeric() and using another conditional statement, rather than in one condition in the second statement.

Additionally, you could add an extra condition to check if the inputs are left empty, and adding required to each input, but don't rely on this solely.

if( (!isset($number1,$number2 )) 
    || !is_numeric($number1) 
    || !is_numeric($number2) )  {

        echo "Invalid input ";
       }

References:

NOTE:

Edit: After revisiting the question and during the time I was writing this, noticed you have posted your form.

Since you did not post your HTML form, this is the following that it was tested with:

<?php

// https://stackoverflow.com/q/41418885/

class calculator_oop
{
    public $num1;
    public $num2;
    public $result;
   public function __construct($number1,$number2){
//       if( (!isset($number1,$number2 )) || (empty($number1 || $number2)))  {

  if( (!isset($number1,$number2 )) || !is_numeric($number1) || !is_numeric($number2) )  {
           echo "Invalid input ";
       }
       else{
           $this->num1 = $number1;
           $this->num2 = $number2;
       }
   }
   public function add(){
       return $this->result = $this->num1 + $this->num2;
   }
}

if(isset($_POST['submit'])){

$ob = new calculator_oop($_POST['num1'],$_POST['num2']);
if($_POST['add'] =='+' ){
    echo $ob-> add();
    }

}

?>

<form action="" method="post">

Number 1: 
<input type="text" name="num1">
<br>
Number 2: 
<input type="text" name="num2">
<br>

<input type="text" name="add" value="+" readonly>

<br>

<input type="submit" name="submit" value="Submit">

</form>

brother i took your code but it didn't full fill the requirement. please check this out if i blank all the field than it shows the invalid input but there is an extra 0 after the invalid input. plz check this out. other wise your answer is very helpful. :) — Ariful Haque Anna, Jan 02 '17 at 05:11

why i get an default output 0 after the invalid inputs?

2 Answers2