PHP Set 2

Question 1

What is the difference between the ‘==’ and the ‘===’ comparison operators?

Answer 1

== is true iff expr1 is equal to expr2 after type juggling
=== is true iff expr1 is equal to expr2 and they are of the same type

Ex: “1.23e2” == 123 is true but “1.23e2” === 123 is false

Question 2

What is the difference between the != and !== comparison operators?

Answer 2

!= is true iff expr1 is not equal to expr2 after type juggling
!== is true iff expr1 is not equal to expr2 or they are not of the same type

Ex: “123” != 123 is false but “123” !== 123 is true

Question 3

Do the < and > comparison operators perform type juggling?

Answer 3

Yes, <, <=, >, and >= all perform type juggling before being evaluated

Question 4

How can strings be compared in PHP?

Answer 4

Using strcmp(expr1, expr2)
Using the three-way comparison operator only available in PHP 7

Question 5

How does the three-way comparison operator work?

Answer 5

expr1 <=> expr2
Returns -1 if expr1 < expr2
Returns 1 if expr1 > expr2
Returns 0 if expr1 == expr2

Question 6

What does strcmp(expr1, expr2) return?

Answer 6

< 0 if expr 1 < expr2
> 0 if expr1 > expr2
0 if expr1 == expr2

Question 7

What are the 3 functions available in PHP to test if a value is NAN or INF?

Answer 7

is_nan(value) returns TRUE if a value is NAN
is_infinite(value) returns TRUE if a value is INF or -INF
is_finite(value) returns true if a value is neither NAN nor INF/-INF

Question 8

What are the rules for keys and values for an associative array in PHP?

Answer 8

Keys can be integers or strings and values can be of any type including arrays

Keys are not necessarily unique

Question 9

What function gives you the size of an array?

Answer 9

count(array $value, int $mode)
The mode can be COUNT_NORMAL which it is by default or COUNT_RECURSIVE which is particularly useful for counting elements of a multidimensional array

Question 10

How can you retrieve the keys and values of an array separately?

Answer 10

Using the array_keys method you can get the keys in number-indexed array form
Using the array_values method you can get the values in number-indexed array form

Question 11

How can you check if a particular key exists within an array?

Answer 11

Using the array_key_exists(key, array) function

Question 12

What is the syntax for a foreach loop?

Answer 12

foreach($array as $key=>$value) {
}
Note that $key=> is optional

Question 13

How can you add elements to an array?

Answer 13

Using array_push($array, value1, value2, …) you can add one or more values onto the end of an array

Question 14

How can you remove elemtns from an array?

Answer 14

Using array_pop($array) you can remove the last element from an array and return it

Question 15

What happens if you try to use array_pop on an empty array or something that is not an array?

Answer 15

NULL will be returned

Question 16

How can you remove an element from the front of an array?

Answer 16

Using array_shift($array) will remove the first element from the array and return it

Question 17

What happens if you try to use array_shift on an empty array or something that is not an array?

Answer 17

NULL will be returned

Question 18

How can you prepend elements to an array?

Answer 18

Using array_unshift($array, value1, value2,…) you can prepend one or more values to the beginning of the array

Question 19

What does array_unshift and array_push return?

Answer 19

Returns the new number of elements in the array

Question 20

What is variable scope?

Answer 20

The context in which a variable is defined and used