Какого оператора нет в php
Арифметические операторы подчиняются математическим законам!
Если написано, что d = a + b * c, то вначале произойдёт умножение, а потом уже сложение.
Если сталкиваются несколько выражений с плюсом и минусом, то ставятся простые скобки ().
Внимательный читатель должен был увидеть, что нет знака равно » height_25″>Скопировать ссылку
Операторы сравнения в PHP.
Операторы сравнения относятся к логическим операторам, и применяются для сравнения переменных. Массивы и объекты с их помощью сравнивать нельзя.
Логические операторы в PHP.
Если нужно объединить или сократить код, «и», «или», «если не», применяются логические операторы. В большинстве случаев используются в условиях.
Operators
An operator is something that takes one or more values (or expressions, in programming jargon) and yields another value (so that the construction itself becomes an expression).
Operators can be grouped according to the number of values they take. Unary operators take only one value, for example ! (the logical not operator) or ++ (the increment operator). Binary operators take two values, such as the familiar arithmetical operators + (plus) and — (minus), and the majority of PHP operators fall into this category. Finally, there is a single ternary operator, ? : , which takes three values; this is usually referred to simply as «the ternary operator» (although it could perhaps more properly be called the conditional operator).
A full list of PHP operators follows in the section Operator Precedence. The section also explains operator precedence and associativity, which govern exactly how expressions containing several different operators are evaluated.
User Contributed Notes 9 notes
of course this should be clear, but i think it has to be mentioned espacially:
’cause || has got a higher priority than and, but less than &&
of course, using always [ && and || ] or [ AND and OR ] would be okay, but than you should at least respect the following:
the first code will set $a to the result of the comparison $b with $c, both have to be true, while the second code line will set $a like $b and THAN — after that — compare the success of this with the value of $c
maybe usefull for some tricky coding and helpfull to prevent bugs 😀
Operator are used to perform operation.
Operator are mainly divided by three groups.
1.Uniary Operators that takes one values
2.Binary Operators that takes two values
3.ternary operators that takes three values
Operator are mainly divided by three groups that are totally seventeen types.
1.Arithmetic Operator
+ = Addition
— = Subtraction
* = Multiplication
/ = Division
% = Modulo
** = Exponentiation
2.Assignment Operator
= null coalescing
14.Clone new Operator
clone new = clone new
16.yield Operator
yield = yield
17.print Operator
print = print
Other Language books’ operator precedence section usually include «(» and «)» — with exception of a Perl book that I have. (In PHP «<" and ">» should also be considered also). However, PHP Manual is not listed «(» and «)» in precedence list. It looks like «(» and «)» has higher precedence as it should be.
Note: If you write following code, you would need «()» to get expected value.
$bar = true ;
$str = «TEST» . ( $bar ? ‘true’ : ‘false’ ) . «TEST» ;
?>
Without «(» and «)» you will get only «true» in $str.
(PHP4.0.4pl1/Apache DSO/Linux, PHP4.0.5RC1/Apache DSO/W2K Server)
It’s due to precedence, probably.
The variable symbol ‘$’ should be considered as the highest-precedence operator, so that the variable variables such as $$a[0] won’t confuse the parser. [http://www.php.net/manual/en/language.variables.variable.php]
If you use «AND» and «OR», you’ll eventually get tripped up by something like this:
$this_one = true ;
$that = false ;
$truthiness = $this_one and $that ;
?>
Want to guess what $truthiness equals?
If you said «false» . it’s wrong!
«$truthiness» above has the value «true». Why? «=» has a higher precedence than «and». The addition of parentheses to show the implicit order makes this clearer:
( $truthiness = $this_one ) and $that ;
?>
If you used «&&» instead of and in the first code example, it would work as expected and be «false».
This also works to get the correct value, as parentheses have higher precedence than » default»>$truthiness = ( $this_one and $that );
?>
Note that in php the ternary operator ?: has a left associativity unlike in C and C++ where it has right associativity.
You cannot write code like this (as you may have accustomed to in C/C++):
$a = 2 ;
echo (
$a == 1 ? ‘one’ :
$a == 2 ? ‘two’ :
$a == 3 ? ‘three’ :
$a == 4 ? ‘four’ : ‘other’ );
echo «\n» ;
// prints ‘four’
?>
You need to add brackets to get the results you want:
echo ( $a == 1 ? ‘one’ :
( $a == 2 ? ‘two’ :
( $a == 3 ? ‘three’ :
( $a == 4 ? ‘four’ : ‘other’ ) ) ) );
echo «\n» ;
//prints ‘two’
?>
The scope resolution operator . which is missing from the list above, has higher precedence than [], and lower precedence than ‘new’. This means that self::$array[$var] works as expected.
A quick note to any C developers out there, assignment expressions are not interpreted as you may expect — take the following code ;-
$a =array( 1 , 2 , 3 );
$b =array( 4 , 5 , 6 );
$c = 1 ;
print_r ( $a ) ;
?>
This will output;-
Array ( [0] => 1 [1] => 6 [2] => 3 )
as if the code said;-
$a[1]=$b[2];
Under a C compiler the result is;-
Array ( [0] => 1 [1] => 5 [2] => 3 )
as if the code said;-
$a[1]=$b[1];
It would appear that in php the increment in the left side of the assignment is processed prior to processing the right side of the assignment, whereas in C, neither increment occurs until after the assignment.
A variable is a container that contain different types of data and the operator operates a variable correctly.
- Language Reference
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- Types
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- Operators
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- References Explained
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