James Tombs Development blog about PHP, HTML & CSS and Drupal

There are a few different types of operators in PHP and I will cover the most commonly used ones.

Arithmetic Operators

These are list basic maths. The 4 most common are:

Addition

Sum of $a and $b.

<?php
$a = 4;
$b = 3;
echo $a + $b;
?>

Outputs:

7

Subtraction

Difference of $a and $b.

<?php
$a = 4;
$b = 3;
echo $a - $b;
?>

Outputs:

1

Multiplication

Product of $a and $b.

<?php
$a = 4;
$b = 3;
echo $a * $b;
?>

Outputs:

12

Division

Quotient of $a and $b.

<?php
$a = 4;
$b = 3;
echo $a / $b;
?>

Outputs:

1.33333333333

Assignment

An assignment operator assigns a value to a variable name.

<?php
$a = ($b = 10) + 5;
?>

With this $a equals 15 and $b is set to 10.

<?php
$a = 10;
$a += 5;
$b = "hello ";
$b .= "world!";
?>

$a is initially set to 10, then is changed to 15. $b is initially set to ‘hello ‘ then ‘hello world!’ by using the period before the equals (.=).

Comparison

Comparison operators compare 2 values. These are often used in if statements, for example: if $a equals $b then do this.

$a == $b

Returns TRUE if $a is equal to $b.

<?php
$a = 3;
$b = 3;
$c = 2;
var_dump($a == $b); // 3 == 3 is true
var_dump($b == $c); // 3 == 2 is false
var_dump(0 == "s"); // 0 == 0 is true
var_dump("1" == "01"); // 1 == 1 is true
var_dump("1" == "1e0"); // 1 == 1 is true
?>

$a === $b

Returns TRUE if $a is identical to $b.

<?php
$a = 3;
$b = 3;
$c = 2;
var_dump($a === $b); // 3 === 3 is true
var_dump($b === $c); // 3 === 2 is false
var_dump(0 === "s"); // 0 === 0 is false
var_dump("1" === "01"); // 1 === 1 is false
var_dump("1" === "1e0"); // 1 === 1 is false
?>

$a != $b, $a <> $b

Returns TRUE if $a is not equal to $b.

<?php
$a = 3;
$b = 3;
$c = 2;
var_dump($a != $b); // 3 != 3 is false
var_dump($b <> $c); // 3 <> 2 is true
var_dump(0 != "s"); // 0 != 0 is false
var_dump("1" != "01"); // 1 !=1 is false
var_dump("1" <> "1e0"); // 1 <> 1 is false
?>

$a !== $b

Returns TRUE if $a is not identical to $b.

<?php
$a = 3;
$b = 3;
$c = 2;
var_dump($a !== $b); // 3 !== 3 is false
var_dump($b !== $c); // 3 !== 2 is true
var_dump(0 !== "s"); // 0 !== 0 is true
var_dump("1" !== "01"); // 1 !== 1 is true
var_dump("1" !== "1e0"); // 1 !== 1 is true
?>

$a < $b

Returns TRUE if $a is less than $b.

<?php
$a = 3;
$b = 3;
$c = 2;
var_dump($a < $b); // 3 < 3 is false
var_dump($b < $c); // 3 < 2 is false
var_dump(0 < "s"); // 0 < 0 is false
var_dump("1" < "01"); // 1 < 1 is false
var_dump("1" < "1e0"); // 1 < 1 is false
?>

$a > $b

Returns TRUE if $a is greater than $b.

<?php
$a = 3;
$b = 3;
$c = 2;
var_dump($a > $b); // 3 > 3 is true
var_dump($b > $c); // 3 > 2 is true
var_dump(0 > "s"); // 0 > 0 is false
var_dump("1" > "01"); // 1 > 1 is false
var_dump("1" > "1e0"); // 1 > 1 is false
?>

$a <= $b

Returns TRUE if $a is less than or equal to $b.

<?php
$a = 3;
$b = 3;
$c = 2;
var_dump($a <= $b); // 3 <= 3 is true
var_dump($b <= $c); // 3 <= 2 is false
var_dump(0 <= "s"); // 0 <= 0 is true
var_dump("1" <= "01"); // 1 <= 1 is true
var_dump("1" <= "1e0"); // 1 <= 1 is true
?>

$a >= $b

Returns TRUE if $a is greater than or equal to $b.

<?php
$a = 3;
$b = 3;
$c = 2;
var_dump($a >= $b); // 3 >= 3 is true
var_dump($b >= $c); // 3 >= 2 is true
var_dump(0 >= "s"); // 0 >= 0 is true
var_dump("1" >= "01"); // 1 >= 1 is true
var_dump("1" >= "1e0"); // 1 >= 1 is true
?>

Incrementing/Decrementing

Incrementing/Decrementing operators come in 2 forms, pre- and post-increment and decrement.

<?php
echo "Postincrement\n";
$a = 5;
echo "Should be 5: " . $a++ . "\n";
echo "Should be 6: " . $a . "\n";
 
echo "Preincrement\n";
$a = 5;
echo "Should be 6: " . ++$a . "\n";
echo "Should be 6: " . $a . "\n";
 
echo "Postdecrement\n";
$a = 5;
echo "Should be 5: " . $a-- . "\n";
echo "Should be 4: " . $a . "\n";
 
echo "Predecrement\n";
$a = 5;
echo "Should be 4: " . --$a . "\n";
echo "Should be 4: " . $a . "\n";
?>

Outputs:

Postincrement
Should be 5: 5
Should be 6: 6
Preincrement
Should be 6: 6
Should be 6: 6
Postdecrement
Should be 5: 5
Should be 4: 4
Predecrement
Should be 4: 4
Should be 4: 4

Logical

Logical operators return TRUE when variables match given the operator.

$a and $b, $a && $b

<?php
$a = 3;
$b = 3;
$c = 0;
var_dump($a and $b); // Returns true
var_dump($a and $c); // Returns false
var_dump($b && $c); // Returns false
?>

$a or $b, $a || $b

<?php
$a = 3;
$b = 3;
$c = 0;
var_dump($a or $b); // Returns true
var_dump($a or $c); // Returns true
var_dump($b || $c); // Returns true
?>

$a xor $b

<?php
$a = 3;
$b = 3;
$c = 0;
var_dump($a xor $b); // Returns false
var_dump($a xor $c); // Returns true
var_dump($b xor $c); // Returns true
?>

!$a

<?php
$a = 3;
$b = 3;
$c = 0;
var_dump(!$a); // Returns false
var_dump(!$b); // Returns false
var_dump(!$c); // Returns true
?>

String

String operators are the same as some of the assignment operators.

<?php
$a = "Hello ";
$b = $a . "World!"; // now $b contains "Hello World!"
 
$a = "Hello ";
$a .= "World!"; // now $a contains "Hello World!"
?>

The first use the concatenation operator (period) to concatenate both strings together. The second uses the concatenation assignment operator which appends the 2nd argument to the first.

For more information about operators in PHP, visit the PHP.net website which lists more operators and their uses.

Syntax

When writing PHP code it is best to use the following opening and closing statements:

<?php
?>

On some websites and scripts you may see it written like this:

<?
?>

This is not good practice as not all servers will be set up to allow this shorthand tag.

File extension

Files with PHP in should generally have the file extension .php but depending on the server configuration, other extensions can be used such as .php3, .php4, .php5, .html and more.

Closing statements

All commands and statements in PHP have to be closed before you can make another so that PHP knows where one item ends and the next one starts.

For example, an echo statement should end with a semi-colon:

<?php
echo "hello";
?>

Where as an if statement just needs curly brackets around it:

<?php
if ($item > 4) {
  echo $item.'<br />';
}
?>

Comments

Comments in PHP can be done in a few ways.

Single line comments

Single line comments are comments that only span one row, in our echo statement above we could add a comment after the echo to explain what our node does.

<?php
echo "hello"; // prints out hello on the screen
?>

All the user will see on their screen and the source code (when viewing source from their browser) for this is:

hello

We can also stop code from showing by adding comments before the line of code.

<?php
// echo "hello";
?>

In this case the user won’t see anything as we have commented out the line.

You can also use the following for single line comments:

<?php
# echo "hello";
?>

Multi line comments

Multi line comments are comments that span more than one line by using:

<php
/* This is the first line of our comment
  followed by another line
  and finally a third line */
echo "hello";
?>

You can also use this commenting way to take out blocks of code temporarily, like so:

<?php
/*
if ($item > 4) {
  echo $item.'<br />';
}
*/
?>

Whitespace

Much like HTML, whitespace is not important and is ignored and is purely for the presentation to the developer. The following 2 bits of code both produce the same HTML.

<?php
echo "hello";
echo "hello";
?>

Outputs:

hellohello

<?php
echo "hello";
 
 
 
 
 
echo "hello";
?>

Outputs:

hellohello

Variables

Variables are what you can use to store bits of information to reuse them later on in your script. For example:

<?php
$variable_name = 'value';
echo $variable_name;
?>

Outputs:

value

Variable names have certain restrictions that you must keep to for your script to work as expected.

• Must start with either a letter or an underscore (_)
• Must only contain alphanumerics (A-z (upper and lower), 0-9 and underscore (_)
• Variables are case sensitive. $myVar is different to $myvar

Outputting data

There are 2 basic ways of outputting strings and variables. These are echo and print. For the sake of argument they are exactly the same until you get more advanced in PHP and even then you may not have any use for the extra ability of print.

<?php
print 'hello<br />';
echo 'hello';
?>

Outputs:

hello
hello

I tend to stick to using echo.

Echoing strings and variables

The format of echoing strings and variables does confuse a lot of people and early on it is understandable.

1
2
3
4
5

<?php
echo "This is a statement with \"a quote in\".<br />";
echo 'This is a statement with "a quote in".<br />';
echo 'This is a statement with \'a quote in\'.<br />';
?>

Take note of the format of both of the above lines. Line 2 is enclosed using ” ” whereas line 3 is using ‘ ‘. If you have to use quotation marks within a string then you should either enclose the string with the alternative quotes or escape them with the backwards slash (\).

Echoing strings can have it’s moments too. Example:

<?php
$myVar = 'this is a string';
echo 'Variable: $myVar<br />';
echo 'Variable: '.$myVar.'<br />';
echo "Variable: $myVar<br />";
echo "Variable: ".$myVar."<br />";
?>

Outputs:

Variable: $myVar
Variable: this is a string
Variable: this is a string
Variable: this is a string

From the output we can see the last 3 echo statements are correct and we get the result we expect. But the first one does not. This is because variables can’t be called from within ‘ ‘ quotes but they can be called from within ” ” quotes.

To get around this we close the ‘ ‘ and use a . (dot, full stop, period) to concatenate the variable to the string.

Double quotes are also more helpful if using certain escaped characters.

<?php
echo "this\nis\na\nnew\nline";
echo 'this\nis\na\nnew\nline';
?>

Outputs:

this is a new line
this\nis\na\nnew\nline

Source code:

this
is
a
new
line<br />this\nis\na\nnew\nline

Other enclosed characters include:

• Newline: \n
• Carriage return: \r
• Tab: \t
• Dollar: \$
• Double quote: \”

In the case of a backwards slash being used before a character not shown in the list above the backwards slash will be shown as well as the letter succeeding it, example:

<?php
echo "\s";
?>

Outputs:

\s