The == operator compares variable1 to variable2 to see whether they are equal.. === Identical Syntax variable1 === variable2 Description The === operator compares variable1 to variab
Trang 1The == operator compares variable1 to variable2 to see whether they are equal If they are, true is returned
=== (Identical)
Syntax
variable1 === variable2
Description
The === operator compares variable1 to variable2 to see whether they are
identical and are of the same data type If they are, true is returned
$num1 = 5;
$num2 = 5;
$string = "5";
$result1 = ($num1 === $num2); // returns 1
$result2 = ($num1 === $string); // returns 0
!= (Not Equal)
Syntax
variable1 != variable2
Description
The != operator compares variable1 to variable2 to see whether they are not
equal If they are not equal, true is returned
< (Less Than)
Syntax
variable1 < variable2
Description
Trang 2> (Greater Than)
Syntax
variable1 > variable2
Description
The > operator checks whether variable1 is greater than variable2 If so, true is
returned
<= (Less Than or Equal)
Syntax
variable1 <= variable2
Description
The <= operator checks whether variable1 is less than or equal to variable2 If
so, true is returned
$num1 = 5;
$num2 = 4;
$result = ($num1 <= $num2); // returns 0
>= (Greater Than or Equal)
Syntax
variable1 >= variable2
Description
The >= operator checks to see if variable1 is greater than or equal to variable2 If
so, true is returned
Incrementing and Decrementing
Trang 3The incrementing and decrementing operators are used to increase or decrease the values of the items to which they are applied This process can occur in a pre- or post- timeframe, and is most often used to increase or decrease counters, such as in loops
++num (Pre-Increment)
Syntax
++num
Description
The ++ num operator increases the value of num by one If num =0 and ++ num is
applied, num will now equal 1 Because the ++ operator is applied before num , the
increase is applied before anything else For instance, if you tried to print ++ num
when num =0, it would print 1 This is the opposite of post-increment, where 0 would
be printed and the value would be adjusted after the print statement
num (Pre-Decrement)
Syntax
num
Description
The num operator decreases the value of num by one If num =1 and num is
applied, num will now equal 0 Because the operator is applied before num, the decrease is applied before anything else For instance, if you tried to print num when num=1, it would print 0 This is the opposite of post-decrement, where 1 would
be printed and the value would be adjusted after the print statement
num++ (Post-Increment)
Syntax
num++
Description
Trang 4The num ++ operator increases the value of num by one If num =0 and num ++ is applied, num will now equal 1 Because the ++ operator is applied after num , the
increase is applied after anything else For instance, if you tried to print num++ when
num =0, it would print 0 This is the opposite of pre-increment, where 1 would be printed and the value would be adjusted before the print statement
num (Post-Decrement)
Syntax
num
Description
The num operator decreases the value of num by one If num =1 and num is applied, num will now equal 0 Because the operator is applied after num, the decrease is applied after anything else For instance, if you tried to print num when num =1, it would print 1 This is the opposite of pre-decrement where 0 would
be printed and the value would be adjusted before the print statement
Other
Some groups of operators, such as error control, have only one language element in them For organization reasons, we have included these items in this section of this chapter
@ (Error Control)
Syntax
@expression
Description
The @ operator, which can be prepended to any PHP expression, tells the interpreter
to ignore any error messages that it might encounter
Note
Any errors that are encountered will be stored in the $php_errormsg variable if the track_errors option is set in the configuration file If there
is an error, this enables you to stop the program, access the error, and write it to the page See the die() entry in Chapter 5, "PHP Language Extensions," for more information
Trang 5` ` (Execution)
Syntax
`command`
Description
The ` ` operator will attempt to execute the shell command If you set a variable
equal to this operator, the results of running command will be stored in the variable
Warning
These are backticks, not single quotes
Logical
Logical operators are very similar to comparison operators and are used to evaluate Boolean expressions When using this type of operator, it is important to understand the corresponding truth tables In this section of the chapter, we discuss these operators and each entry will contain its corresponding truth table
and
Syntax
variable1 and variable2
Description
The and operator evaluates whether both variable1 and variable2 are true, or
equal Table 4.5 contains the truth table for the possible values In understanding the truth table, you can see the only time the equation returns true is when both
variable1 and variable2 are true
Note
The only difference between this operator and the && operator is order