arguments - Reference — What does this symbol mean in PHP?

Question

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This is a collection of questions that come up every now and then about syntax in PHP. This is also a Community Wiki, so everyone is invited to participate in maintaining this list.

Why is this?

It used to be hard to find questions about operators and other syntax tokens.1
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If you have been pointed here by someone because you have asked such a question, please find the particular syntax below. The linked pages to the PHP manual along with the linked questions will likely answer your question then. If so, you are encouraged to upvote the answer. This list is not meant as a substitute to the help others provided.

The List

If your particular token is not listed below, you might find it in the List of Parser Tokens.

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& Bitwise Operators or References

• What does it mean to start a PHP function with an ampersand?
• Understanding PHP & (ampersand, bitwise and) operator
• PHP "&" operator
• Difference between & and && in PHP
• What does "&" mean here in PHP?
• What does "&" mean in this case?
• What does the "&" sign mean in PHP?
• What does this signature mean (&) in PHP?
• How does the "&" operator work in a PHP function?
• What does & in &2 mean in PHP?
• When should I use a bitwise operator?
• Is there ever a need to use ampersand in front of an object? (&$)

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=& References

• Reference assignment operator in PHP, =&
• What do the "=&" and "&=" operators in PHP mean?
• What do the '&=' and '=&' operators do?
• What does =& mean in PHP?

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&= Bitwise Operators

• What do the "=&" and "&=" operators in PHP mean?
• What do the '&=' and '=&' operators do?

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&& Logical Operators

• 'AND' vs '&&' as operator
• Difference between & and && in PHP
• Is there any difference between "and" and "&&" operators in PHP?
• PHP - and / or keywords

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% Arithmetic Operators

• What does the percent sign mean in PHP?
• What is the PHP operator % and how do I use it in real-world examples?

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!! Logical Operators

• Double not (!!) operator in PHP

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@ Error Control Operators

• What is the use of the @ symbol in PHP?
• 'At' symbol before variable name in PHP: @$_POST
• PHP functions and @functions
• Should I use @ in my PHP code?
• What does @ mean in PHP?

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?: Ternary Operator

• What are the PHP operators "?" and ":" called and what do they do?
• ?: operator (the 'Elvis operator') in PHP
• Where can I read about conditionals done with "?" and ":" (colon)?
• Using PHP 5.3 ?: operator

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?? Null Coalesce Operator (since PHP 7)

• C#'s null coalescing operator (??) in PHP

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?string ?int ?array ?bool ?float Nullable return type declaration (since PHP 7.1)

• Nullable return type declaration
• php method argument type hinting with question mark (?type)

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: Alternative syntax for control structures, Ternary Operator, Return Type Declaration

• What is ":" in PHP?
• What does ":" mean in PHP?
• Colon after method declaration?

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:: Scope Resolution Operator

• What do two colons mean in PHP?
• What's the meaning of the PHP token name T_PAAMAYIM_NEKUDOTAYIM?
• What's the difference between :: (double colon) and -> (arrow) in PHP?
• What exactly are late static bindings in PHP?
• static::staticFunctionName()
• Unexpected T_PAAMAYIM_NEKUDOTAYIM, expecting T_NS_Separator

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Namespaces

• Backslash in PHP -- what does it mean?
• What does a (backslash) do in PHP (5.3+)?

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-> Classes And Objects

• What is the "->" PHP operator called?
• Where do we use the object operator "->" in PHP?
• What's the difference between :: (double colon) and -> (arrow) in PHP?
• What does the PHP syntax $var1->$var2 mean?
• What does "->" mean/refer to in PHP?

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=> Arrays

• What does "=>" mean in PHP?
• Use of => in PHP
• What does $k => $v in foreach($ex as $k=>$v) mean?

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^ Bitwise Operators

• How does the bitwise operator XOR ('^') work?
• What does ^ mean in PHP?

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>> Bitwise Operators

• What does >> mean in PHP?

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<< Bitwise Operators

• Strange print behaviour in PHP?
<

Answer 1

Incrementing / Decrementing Operators

++ increment operator

-- decrement operator

Example    Name              Effect
---------------------------------------------------------------------
++$a       Pre-increment     Increments $a by one, then returns $a.
$a++       Post-increment    Returns $a, then increments $a by one.
--$a       Pre-decrement     Decrements $a by one, then returns $a.
$a--       Post-decrement    Returns $a, then decrements $a by one.

These can go before or after the variable.

If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.

For example:

$apples = 10;
for ($i = 0; $i < 10; ++$i) {
    echo 'I have ' . $apples-- . " apples. I just ate one.
";
}

Live example

In the case above ++$i is used, since it is faster. $i++ would have the same results.

Pre-increment is a little bit faster because it really increments the variable and after that 'returns' the result. Post-increment creates a special variable, copies there the value of the first variable and only after the first variable is used, replaces its value with second's.

However, you must use $apples--, since first, you want to display the current number of apples, and then you want to subtract one from it.

You can also increment letters in PHP:

$i = "a";
while ($i < "c") {
    echo $i++;
}

Once z is reached aa is next, and so on.

Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.

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Stack Overflow Posts:

• Understanding Incrementing