The if statement doesn't work for false in php

Question

When trying to get familiar with if statement in PHP, this happened. First time i tried this code below.

if(true) {echo 'true';} else {echo 'false';}

And the output was true when the condition is true. Again, when the condition is false (if(false)) it echos false.

But i tried the same, using a variable as the condition, while changing the value of the variable.

$con='false';
if($con){echo 'true';} else{echo 'false';} 

At this situation the output is true even when the variable value is false or true. At the same time, the if statement working fine when 1 and 0 is used instead true and false. Why is this happening?

Answer 1

$con='false';

That 'false' is a valid string which is not Boolean FALSE, just like $con='hi'; isn't.

$con=FALSE;  //this is false now

To quote from the Manual

To specify a boolean literal, use the constants TRUE or FALSE. Both are case-insensitive.

Also read these other options that you have

When converting to boolean, the following values are considered FALSE:

◦ the boolean FALSE itself
◦ the integer 0 (zero)
◦ the float 0.0 (zero)
◦ the empty string, and the string "0"
◦ an array with zero elements
◦ an object with zero member variables (PHP 4 only)
◦ the special type NULL (including unset variables)
◦ SimpleXML objects created from empty tags

Then you observed this

At the same time, the if statement working fine when 1 and 0 is used instead true and false. Why is this happening?

This is because 0 in any form is FALSE, either string or numeric. But the text false as a string is not false for reasons mentioned above.

Also read about PHP Strict Comparisons since you're learning, because

var_dump(0==FALSE);    //bool(true)
var_dump(0===FALSE);   //bool(false)   :)

Answer 2

PHP does some sneaky things in the if expression. The following values are considered FALSE:

• the boolean FALSE itself
• the integer 0 (zero)
• the float 0.0 (zero)
• the empty string, and the string "0"
• an array with zero elements
• an object with zero member variables (PHP 4 only)
• the special type NULL (including unset variables)
• SimpleXML objects created from empty tags

Every other value is considered TRUE (including any resource).

You're actually passing a string that says the word false, rather than the value false itself. Because that isn't in the above list, it is actually considered true!

Answer 3

As described in the section about expressions, expression is evaluated to its Boolean value. If expression evaluates to TRUE, PHP will execute statement, and if it evaluates to FALSE - it'll ignore it. More information about what values evaluate to FALSE can be found in the 'Converting to boolean' section.

So as per docs try using

$con = false;//boolean and not a string
if($con){echo 'true';} else{echo 'false';} 

When converting to boolean, the following values are considered FALSE:

◦ the boolean FALSE itself
◦ the integer 0 (zero)
◦ the float 0.0 (zero)
◦ the empty string, and the string "0"
◦ an array with zero elements
◦ an object with zero member variables (PHP 4 only)
◦ the special type NULL (including unset variables)
◦ SimpleXML objects created from empty tags

Check Docs (IF MANUAL)