Page 84 - Beginning PHP 5.3

Part II: Learning the Language
Now that you know how Boolean values work you can start combining Boolean values with logical
operators. PHP features six logical operators, and they all work in combination with true or false
Boolean values to produce a result of either true or false :

Operator Example Result

& & (and) $x & & $y true if both $x and $y evaluate to true ; false otherwise

and $x and $y true if both $x and $y evaluate to true ; false otherwise
|| (or) $x || $y true if either $x or $y evaluates to true ; false otherwise

or $x or $y true if either $x or $y evaluates to true ; false otherwise
xor $x xor $y true if $x or $y (but not both) evaluates to true ; false
otherwise
! (not) !$x true if $x is false ; false if $x is true

Here are some simple examples of logical operators in action:
$x = 2;
$y = 3;
echo ( ($x > 1) & & ($x < 5) ) . “ < br / > ”; // Displays 1 (true)

echo ( ($x == 2) or ($y == 0) ) . “ < br / > ”; // Displays 1 (true)
echo ( ($x == 2) xor ($y == 3) ) . “ < br / > ”; // Displays “” (false) because both
// expressions are true
echo ( !($x == 5 ) ) . “ < br / > ”; // Displays 1 (true) because
// $x does not equal 5
The main use of logical operators and Boolean logic is when making decisions and creating loops, which
you explore in Chapter 4 .

You ’ re probably wondering why the and and or operators can also be written as & & and || . The reason is
that and and or have a different precedence to & & and || . Operator precedence is explained in a moment.
String Operators
There ’ s really only one string operator, and that ’ s the concatenation operator , . (dot). This operator simply
takes two string values, and joins the right - hand string onto the left - hand one to make a longer string.

For example:
echo “Shaken, “ . “not stirred”; // Displays “ Shaken, not stirred ”

You can also concatenate more than two strings at once. Furthermore, the values you concatenate don ’ t
have to be strings; thanks to PHP ’ s automatic type conversion, non - string values, such as integers and
floats, are converted to strings at the time they ’ re concatenated:

$tempF = 451;
// Displays “ Books catch fire at 232.777777778 degrees C. ”
echo “Books catch fire at “ . ( (5/9) * ($tempF - 32) ) . “ degrees C.”;

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