Strange IF Statement behaviour

Question

Hello All,

I have an IF statement that consists of two separate function calls passing values to two variables. Obviously if neither value is 'FALSE' then the code block is executed:

<?php
   class MyValidater {
      static function validateString($string) {
         if (preg_match("/[A-Za-z]+/", $string)) {
            return $string;
         } else {
            return false;
         }
      }
   }

   $firstName = "Daniel";
   $surname = "Simmons";

   // Dodgy IF statement
   if ($first = MyValidater::validateString($firstName) && $second = MyValidater::validateString($surname)) {
      print("Success: $first $second");
   } else {
      print("Fail: $first $second");
   }
?>

As you can see both the $first and $second variables should contain the values held in $firstName and $surname after successfully being validated by the Static method validateString.

However, the values of the two variables end up: $first = '1' and $second = "Simmons".

The '1' should be "Daniel" but for some reason $first is being passed the value '1' or TRUE. If you swap the two assignment statements over so that $second is evaluated first, you end up with the opposite outcome as before. $second = '1' and $first = "Daniel"

Can anyone explain why the String value "Daniel" being returned from the class method is being changed into the int '1' for the first part of the conditional statement only? I have had a quick look though the PHP documentation but cannot find an explanation.

For the moment the workaround is to change the return value from the static method to be true/false and then make $first = $firstName, etc... upon success. But this involves more code and I would rather find out why this way does not work.

Thanks,

Dan

Answer 1

You need to bracket your expressions:

if (($first = MyValidater::validateString($firstName)) && ($second = MyValidater::validateString($surname)))

What's actually happening is this:

if ($first = (MyValidater::validateString($firstName) && $second = MyValidater::validateString($surname)))

It would be much clearer to just do this (note this code isn't identical to what you have):

$first = MyValidater::validateString($firstName);
$second = MyValidater::validateString($surname);

if ($first && $second)

Answer 2

Try using parenthesis

($first = MyValidater::validateString($firstName)) && ($second = MyValidater::validateString($surname)))

First is getting the result of the first function call AND the second function having a value.

Answer 3

= is for attributions
== is for comparisons, the data type doesn't matter
=== is for comparisons, the data type matters

Answer 4

&& is higher then = in the operator precedence. add brackets and it will work.

http://www.php.net/manual/en/language.operators.precedence.php

you can read about operator precedence here.

Also, setting values inside of an if condition is usually bad practice. If you add the brackets, you will most probably see why (let $first set to false and $second set to a string) => the first will be evaluated, but since it is false then, it won't process further since it will go to the else anyways. => second will not be set correct if first = false.

Answer 5

What is happening is that PHP is assigning $first with “MyValidater::validateString($firstName)) && $second = MyValidater::validateString($surname)”

You need brackets around first compare and second, like this.

   if ( ($first = MyValidater::validateString($firstName)) && ($second = MyValidater::validateString($surname))) {