PHP Skills Tests

Operator precedence

PHP's operator precedence:

Associativity	Operators	Additional information
non-associative	clone new	clone and new
left	[	array()
right	**	arithmetic
right	++ -- ~ (int) (float) (string) (array) (object) (bool) @	types and increment/decrement
non-associative	instanceof	types
right	!	logical
left	* / %	arithmetic
left	+ - .	arithmetic and stirng
left	<< >>	bitwise
non-associative	< <= >= >	comparison
non-associative	== != === !== <> <=>	comparison
left	&	bitwise and references
left	^	bitwise
left	`|	bitwise
left	&&	http://php.net/manual/en/language.operators.logical.php logical]
left	||	logical
right	??	comparison
left	? :	ternary
right	= += -= *= /= .= %= &= |= ^= <<= >>= =>	assignment
left	and	logical
left	xor	logical
left	or	logical
left	,`	many uses

Examples

echo 5 * 6 / 2 + 2 * 3; /* <<< result is 21 */
/**
 * Multiplication, division, and modulus have precedence over addition and subtraction.
 * Operations are performed left to right for operators with equal precedence.
 * So 5 * 6 = 30, 30 / 2 = 15, 2 * 3 = 6, and 15 + 6 = 21
 * Result is 21.
 */

Associativity

TK

Hexidecimal values

echo 0x500;
1280

This is hexidecimal notation. The value is calculated 0 * 1 = 0 + 0 * 16 = 0 + 5 * 256 = 1280.

Bitwise operators

Example	Name	Result
$a & $b	And	Bits that are set in both $a and $b are set.
`$a | $b	Or (inclusive or)	Bits that are set in either $a or $b are set.
$a ^ $b	Xor (exclusive or)	Bits that are set in $a or $b but not both are set.
~ $a	Not	Bits that are set in $a are not set, and vice versa.
$a << $b	Shift left	Shift the bits of $a $b steps to the left (each step means "multiply by two")
$a >> $b	Shift right	Shift the bits of $a $b` bits to the right (each step means "divide by two")

$a = (1<<0); /* $a = (0001) = (1*1) = 1 */
$b = (1<<1); /* $b = (0010) = (1*2) = 2 */

echo $b | $a; /* (0010 | 0001) = (0011) = ((1*2) + (1*1)) = 3 (bits set in either value are set in the result) */

is_numeric()

• Valid values: "200", ".25e4", "20,2"
• Invalid values: "$200"

Magical constants

Magical constants are constants that change value depending on where in the code they are placed.

The magical constants in PHP:

• __LINE__
• __FILE__
• __DIR__
• __FUNCTION__
• __CLASS__
• __TRAIT__
• __METHOD__
• __NAMESPACE__

Is print() a function?

print() is a language construct.

echo ((function_exists("print"))?("y"):("n")); /* <<< output is "n" */
echo ((function_exists("printf"))?("y"):("n")); /* <<< output is "y" */
echo ((function_exists("echo"))?("y"):("n")); /* <<< output is "n" */