This is my first php program!

Logical Operators
Logical operators provide ways for you to build complex logical expressions. Logical
operators treat their operands as Boolean values and return a Boolean value. There
are both punctuation and English versions of the operators (
||
and
or
are the same
operator). The logical operators are:
Logical AND (
&&
,
and
)
The result of the logical AND operation is
true
if and only if both operands are
true
; otherwise, it is
false
. If the value of the first operand is
false
, the logical
AND operator knows that the resulting value must also be
false
, so the right-
hand operand is never evaluated. This process is called
short-circuiting
, and a
common PHP idiom uses it to ensure that a piece of code is evaluated only if
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This is the Title of the Book, eMatter Edition
Copyright © 2002 O’Reilly & Associates, Inc. All rights reserved.
Expressions and Operators
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something is true. For example, you might connect to a database only if some
flag is not
false
:
$result = $flag and mysql_connect( );
The
&&
and
and
operators differ only in their precedence.
Logical OR (
||
,
or
)
The result of the logical OR operation is
true
if either operand is
true
; other-
wise, the result is
false
. Like the logical AND operator, the logical OR operator
is short-circuited. If the lefthand operator is
true
, the result of the operator must
be
true
, so the righthand operator is never evaluated. A common PHP idiom
uses this to trigger an error condition if something goes wrong. For example:
$result = fopen($filename) or exit( );
The
||
and
or
operators differ only in their precedence.
Logical XOR (
xor
)
The result of the logical XOR operation is
true
if either operand, but not both, is
true
; otherwise, it is
false
.
Logical negation (
!
)
The logical negation operator returns the Boolean value
true
if the operand eval-
uates to
false
, and
false
if the operand evaluates to
true
.