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

Data types

Hexidecimal notation

Hex notation is indicated by a leading 0x

echo 0x500;
1280

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

Octal notation

Octal notation is indicated by a leading zero.

vardump($a = 010); // (1 * pow(8, 1)) = 8

Q: What is the output of the following code?

echo 0500; // (5 * pow(8, 2)) = 5 * 64  = 320

A: 320

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")

Bitwise operators

$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) */

Bitwise operators and precedence

Q: What will be the output of the following code?

$a = (1 << 0); /* $a = (1*1) = 1 */
$b = (1 << $a); /* $b = (1*2) = 2 */
$c = (1 << $b); /* $c = (1*4) = 4 */
echo ($c || $b) << 2 * $a | $a; 
/* ($c || $b) i.e. "4 or 2". Unless they are both false it will evaluated to true. Result is "true", or 1 */
/* multiplication > bitwise shift > bitwise or, in terms of precedence */
/* next operation, multiplication: 2 * $a, or 2 * 1 = 2 */
/* next operation, bitwise shift: 1 << 2 = 4; */
/* next operation, bitwise or: 4 | 1 = 100 | 001 = 5 */

A: 5

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__

Language constructs

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" */

Control structure alternative syntax

Q: Is the following code valid?

$a = 5;
if ($a==5):
    echo "Hello";
    echo "1";
else:
    echo "Not hello";
    echo "2";
endif;

A: Yes

Arrays

Joining array elements into string

Q: What function should you use to join array elements with a glue string?

1. join_str
2. implode
3. connect
4. make_array
5. None of the above

my answer: b. implode

Array comparison operators

Q: When comparing two arrays, what is the difference between == and ===?

1. == compares keys while === compares keys and values
2. === also compares the order and types of the objects
3. === compares the array references
4. They are identical
5. None of the above

A: (b) === also compares the order and types of the objects