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An Intranet Design Magazine Tutorial

By Aaron Weiss

PHP Comparison Operators

Operator	Name	Description	Examples	Yields
==	Equality	Tests whether two expressions are of equal value. For strings, the two must be exactly the same.	$val1 == $val2 $name1 == $name2	false false
!=	Inequality	Tests whether two expressions are not equal, or for strings, not exactly the same.	$val1 != $val2 $name1 != $name2	true true
<	Less than	Tests whether the lefthand expression has a value smaller than the righthand expression. For strings, smaller means "comes before alphabetically".	$val1 < $val2 $name1 < $name2	false true
>	Greater than	Tests whether the lefthand expression has a value greater than the righthand expression. For strings, greater means "comes after alphabetically".	$val1 > $val2 $name1 > $name2	true false
<=	Less than or equal to	Tests whether the lefthand expression is of equal or lesser value than the righthand expression.	$val1 <= 15 $name1 <= "Martin"	true true
>=	Greater than or equal to	Tests whether the lefthand expression is of equal or greater value than the righthand expression.	$val2 >=6 $name2 >= "Manfred"	true true

Let's raise the stakes: comparing two values is one thing, but sometimes you need something more, such as the ability to compare several comparisons! Let's be logical about this, and use PHP's logical operators. Suppose for example that you need to know whether $val1 is of lesser value than $val2, and also whether $name1 is of greater value than $name2.

Remember that each comparison expression yields a true or false value. For the record, PHP does not actually possess true or false values, known as boolean data types. Rather, PHP considers the numeric value zero (0), or the string values "0" or empty "" to be false. Any other value, such as 1, or 3, or "cat", is considered to be true. A logical operator compares these true or false values. For example, using PHP's and logical operator:

($val1 < $val2) and ($name1 > $name2)

Because this code fragment is not a full statement, there is no closing semicolon. Rather, we see parentheses grouping two expressions. The lefthand expression will evaluate to the value false, if we assume the example values used in the comparison operator table. The righthand expression will also be false, since "Martin" does not come after "Michael" alphabetically. The and operator will therefore compare the values "false and false". Because this operator returns true only when both expressions are true, the above expression will ultimately return false. That can be hard to follow, so let's look at a summary table.

PHP Logical Operators >

< Operations and Comparisons