php operator == (sort of equality) and the integer 0
<?php
    print "number of surprised persons: " . ('false' == 0);

number of surprised persons: 1

0        <-- integer
false    <-- boolean
null     <-- just.. you know, null
'0'      <-- string
''       <-- string
'false'  <-- string
'true'   <-- string
'null'   <-- string

'true' == 0
// is the same as
(int)'true' == 0
// is the same as
0 == 0
// is the same as
true

Example     Name     Result
$a == $b    Equal    TRUE if $a is equal to $b after type juggling.

<?php
print "number of surprised persons: " . ('false' == 0.3 - 0.2 - 0.1);

$a = true;
echo "$a"; #1