Operations in PHP

Jeyaseelansarc · #21 (**permalink**) 04-22-2008, 12:56 AM

Comparison operators, as their name implies, allow you to compare two values.
If you compare an integer with a string, the string is converted to a number. If you compare two numerical strings, they are compared as integers. These rules also apply to the switch statement.

PHP Code:

  <?php

var_dump(0 == "a"); // 0 == 0 -> true

var_dump("1" == "01"); // 1 == 1 -> true

 
switch ("a") {

case 0:

    echo "0";

    break;

case "a": // never reached because "a" is already matched with 0

    echo "a";

    break;

}

?>

Jeyaseelansarc · #22 (**permalink**) 04-22-2008, 01:00 AM

Here some of comparison operators
$a == $b -> Equal
$a === $b -> Identical
$a != $b ->Not equal
$a <> $b -> Not equal
$a !== $b ->Not identical
$a < $b ->Less than
$a > $b ->Greater than
$a <= $b ->Less than or equal to
$a >= $b ->Greater than or equal to

Jeyaseelansarc · #23 (**permalink**) 04-22-2008, 01:00 AM

Transcription of standard array comparison

PHP Code:

  <?php

// Arrays are compared like this with standard comparison operators

function standard_array_compare($op1, $op2)

{

    if (count($op1) < count($op2)) {

        return -1; // $op1 < $op2

    } elseif (count($op1) > count($op2)) {

        return 1; // $op1 > $op2

    }

    foreach ($op1 as $key => $val) {

        if (!array_key_exists($key, $op2)) {

            return null; // uncomparable

        } elseif ($val < $op2[$key]) {

            return -1;

        } elseif ($val > $op2[$key]) {

            return 1;

        }

    }

    return 0; // $op1 == $op2

}

?>

Jeyaseelansarc · #24 (**permalink**) 04-22-2008, 01:02 AM

Ternary Operator

Another conditional operator is the "?:" (or ternary) operator.

PHP Code:

  <?php

 // Example usage for: Ternary Operator

 $action = (empty($_POST['action'])) ? 'default' : $_POST['action'];

 
 // The above is identical to this if/else statement

 if (empty($_POST['action'])) {

     $action = 'default';

 } else {

     $action = $_POST['action'];

 }

 
 ?>

The expression (expr1) ? (expr2) : (expr3) evaluates to expr2 if expr1 evaluates to TRUE, and expr3 if expr1 evaluates to FALSE.

Jeyaseelansarc · #25 (**permalink**) 04-22-2008, 01:02 AM

Ternary operator is a statement, and that it doesn't evaluate to a variable, but to the result of a statement. This is important to know if you want to return a variable by reference. The statement return $var == 42 ? $a : $b; in a return-by-reference function will therefore not work and a warning is issued in later PHP versions.

Jeyaseelansarc · #26 (**permalink**) 04-22-2008, 11:27 PM

Error Control Operators

PHP supports one error control operator: the at sign (@). When prepended to an expression in PHP, any error messages that might be generated by that expression will be ignored.

If the track_errors feature is enabled, any error message generated by the expression will be saved in the variable $php_errormsg. This variable will be overwritten on each error, so check early if you want to use it.

Jeyaseelansarc · #27 (**permalink**) 04-22-2008, 11:28 PM

For e.g

PHP Code:

  <?php

/* Intentional file error */

$my_file = @file ('non_existent_file') or

    die ("Failed opening file: error was '$php_errormsg'");

 
// this works for any expression, not just functions:

$value = @$cache[$key]; 

// will not issue a notice if the index $key doesn't exist.

 
?>

Jeyaseelansarc · #28 (**permalink**) 04-22-2008, 11:29 PM

The @-operator works only on expressions. A simple rule of thumb is: if you can take the value of something, you can prepend the @ operator to it. For instance, you can prepend it to variables, function and include() calls, constants, and so forth. You cannot prepend it to function or class definitions, or conditional structures such as if and foreach, and so forth.

Jeyaseelansarc · #29 (**permalink**) 04-22-2008, 11:29 PM

Currently the "@" error-control operator prefix will even disable error reporting for critical errors that will terminate script execution. Among other things, this means that if you use "@" to suppress errors from a certain function and either it isn't available or has been mistyped, the script will die right there with no indication as to why.

senraj · #30 (**permalink**) 05-04-2008, 10:16 PM

Hi,

Binary operators are used on two operands:
2 + 3
14 * 3.1415
$i – 1
These examples are also simple examples of expressions.
PHP can only perform binary operations on two operands that have the
same type. However, if the two operands have different types, PHP automatically
converts one of them to the other’s type, according to the following rules
(unless stated differently, such as in the concatenation operator).

Attachment 201

Booleans, nulls, and resources behave like integers, and they convert in
the following manner:

Boolean: False = 0, True = 1
Null = 0
Resource = The resource’s # (id)

senraj · #31 (**permalink**) 05-05-2008, 04:35 AM

Hi,

Numeric Operators All the binary operators (except for the concatenation operator) work only on numeric operands. If one or both of the operands are strings, Booleans, nulls, or resources, they are automatically
converted to their numeric equivalents before the calculation is performed
(according to the previous table).

Numeric Operators.doc

senraj · #32 (**permalink**) 05-05-2008, 04:36 AM

Hi,

Concatenation Operator (.) The concatenation operator concatenates
two strings. This operator works only on strings; thus, any non-string
operand is first converted to one.
The following example would print out "The year is 2000":
$year = 2000;
print "The year is " . $year;
The integer $year is internally converted to the string "2000" before it is
concatenated with the string’s prefix, "The year is".

senraj · #33 (**permalink**) 05-05-2008, 04:38 AM

Hi,

Assignment operators enable you to write a value to a variable. The first
operand (the one on the left of the assignment operator or l value) must be a
variable. The value of an assignment is the final value assigned to the variable;
for example, the expression $var = 5 has the value 5 (and assigns 5 to
$var).

In addition to the regular assignment operator =, several other assignment
operators are composites of an operator followed by an equal sign. These
composite operators apply the operator taking the variable on the left as the
first operand and the value on the right (the r value) as the second operand,
and assign the result of the operation to the variable on the left.
For example:
$counter += 2; // This is identical to $counter = $counter + 2;
$offset *= $counter;// This is identical to $offset = $offset *
➥$counter;
The following list show the valid composite assignment operators:
+=, -=, *=, /=, %=, ^=, .=, &=, |=, <<=, >>=

senraj · #34 (**permalink**) 05-05-2008, 04:39 AM

Hi,

By-Reference Assignment Operator PHP enables you to create variables
as aliases for other variables. You can achieve this by using the by-reference
assignment operator =&. After a variable aliases another variable, changes to
either one of them affects the other.
For example:
$name = "Judy";
$name_alias =& $name;
$name_alias = "Jonathan";
print $name;
The result of this example is
Jonathan
When returning a variable by-reference from a function (covered later in
this book), you also need to use the assign by-reference operator to assign the
returned variable to a variable:
$retval =& func_that_returns_by_reference();

senraj · #35 (**permalink**) 05-06-2008, 06:13 AM

Hi,

Comparison operators enable you to determine the relationship between
two operands.
When both operands are strings, the comparison is performed lexicographically.
The comparison results in a Boolean value.
For the following comparison operators, automatic type conversions are
performed, if necessary.

Comparison operators.doc

senraj · #36 (**permalink**) 05-06-2008, 06:14 AM

Hi,

Comparison operators

For the following two operators, automatic type conversions are not performed
and, therefore, both the types and the values are compared.

Comparison operators.doc

senraj · #37 (**permalink**) 05-06-2008, 06:28 AM

Hi,

Logical operators first convert their operands to boolean values and then
perform the respective comparison.

Logical Operators.doc

senraj · #38 (**permalink**) 05-06-2008, 06:28 AM

Hi,

Short-Circuit Evaluation When evaluating the logical and/or operators,you can often know the result without having to evaluate both operands.For example, when PHP evaluates 0 && 1, it can tell the result will be false by looking only at the left operand, and it won’t continue to evaluate the right
one. This might not seem useful right now, but later on, we’ll see how we can use it to execute an operation only if a certain condition is met.

senraj · #39 (**permalink**) 05-06-2008, 10:32 PM

Hi,

Bitwise operators perform an operation on the bitwise representation of
their arguments. Unless the arguments are strings, they are converted to
their corresponding integer representation, and the operation is then performed.
In case both arguments are strings, the operation is performed
between corresponding character offsets of the two strings (each character is
treated as an integer).

Bitwise Operators.doc

senraj · #40 (**permalink**) 05-06-2008, 10:36 PM

Hi,

Unary Operators

Unary operators act on one operand.

Negation Operators

Negation operators appear before their operand—for example, !$var (! is the
operator, $var is the operand).

Negation Operators.doc

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
String Operations using different databases	srikumar_l	Database Support	0	12-05-2007 02:27 AM
Date Operations in different databases	srikumar_l