$a == $b Equal - True if $a is equal to $b.
$a === $b Identical - True if $a is equal to $b, and they are of the same type.
$a != $b Not equal - True if $a is not equal to $b.
$a !== $b Not identical - True if $a is not equal to $b, or they are not of the same type.
$a < $b Less than - True if $a is strictly less than $b.
$a > $b Greater than - True if $a is strictly greater than $b.
$a <= $b Less than or equal to - True if $a is less than or equal to $b.
$a >= $b Greater than or equal to - True if $a is greater than or equal to $b.
the ? operator - like the C operator:
<?
echo ($x==0) ? "X value is zero" : "X value is not zero";
?>