PHP why is 0=='all' true? [duplicate]

Question

I am reading the PHP documentation for boolean.

One of the comments says 0=='all' is true.

http://php.net/manual/en/language.types.boolean.php#86809

I want to know how it becomes true.

The documentation says all non-empty strings are true except '0'.

So 'all' is true and 0 is false.

false == true should be false.

But:

if(0=='all'){
    echo 'hello';
}else{
   echo 'how are you ';
}

prints 'hello'.

Answer 1

In PHP, operators == and != do not compare the type. Therefore PHP automatically converts 'all' to an integer which is 0.

echo intval('all');

You can use === operator to check type:

if(0 === 'all'){
    echo 'hello';
}else{
   echo 'how are you ';
}

See the Loose comparisons table.

Answer 2

As you have as left operand an integer, php tries to cast the second one to integer. So as integer representation of a string is zero, then you have a true back. If you switch operators you obtain the same result.

As Bhumi says, if you need this kind of comparison, use ===.