Array count and length in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What function in PHP is used to count the number of elements in an array?

The count() function returns the number of elements in an array.

beginner

What will count([]) return in PHP?

It returns 0 because the array is empty and has no elements.

beginner

How does PHP treat the length of an array compared to the count of an array?

In PHP, the length of an array is the same as the count of its elements. Use count() to get this number.

intermediate

What is the difference between count() and sizeof() in PHP?

Both count() and sizeof() return the number of elements in an array. They are aliases and work the same way.

intermediate

What happens if you use count() on a variable that is not an array?

If the variable is not an array or an object implementing Countable, count() returns 1 if the variable is not null, otherwise 0.

What does count($arr) return if $arr = [1, 2, 3, 4]?

A 1

B 3

C 4

D Error

count() returns the number of elements, which is 4 here.

Which PHP function is an alias of count()?

A length()

B sizeof()

C array_length()

D size()

sizeof() is an alias of count() in PHP.

What will count(null) return in PHP?

A 0

B 1

C null

D Error

count(null) returns 0 because null is treated as empty.

If $arr = ['a' => 1, 'b' => 2], what does count($arr) return?

A 2

B 1

C 0

D Error

Associative arrays count their elements the same as indexed arrays.

Which of these is NOT a valid way to get the number of elements in an array in PHP?

A count($array)

B sizeof($array)

C Both A and B

D length($array)

length() is not a PHP function for arrays.

Explain how to find the number of elements in a PHP array and what happens if the variable is not an array.

Think about the function count() and what it returns for different types.

Describe the difference, if any, between the length of an array and the count of an array in PHP.

Consider how PHP measures array size.

Practice

1. What does the PHP function count() do when used on an array?

easy

A. It returns the number of elements in the array.

B. It returns the sum of all elements in the array.

C. It returns the last element of the array.

D. It sorts the array in ascending order.

Solution

1. Step 1: Understand the purpose of count()

   The count() function in PHP is designed to return how many items are inside an array.

2. Step 2: Compare with other options

   The other options describe summing elements, returning the last element, or sorting the array, which are unrelated to counting elements.

3. Final Answer:

   It returns the number of elements in the array. -> Option A

4. Quick Check:

   count() = number of elements [OK]

Hint: Remember: count() tells how many items, not their values. [OK]

Common Mistakes:

• Thinking count() sums values instead of counting items
• Confusing count() with functions that return elements
• Assuming count() sorts or changes the array

2. Which of the following is the correct syntax to get the number of elements in an array $arr in PHP?

easy

A. length($arr);

B. sizeofArray($arr);

C. size($arr);

D. count($arr);

Solution

1. Step 1: Recall PHP function for array length

   PHP uses count() to get the number of elements in an array.

2. Step 2: Check other options for validity

   Functions like length(), size(), or sizeofArray() do not exist or are incorrect in PHP.

3. Final Answer:

   count($arr); -> Option D

4. Quick Check:

   Use count() for array size [OK]

Hint: Use count() to get array size, not length() or size(). [OK]

Common Mistakes:

• Using length() which is not a PHP function
• Confusing count() with size() or sizeofArray()
• Adding semicolon inside function parentheses

3. What will be the output of the following PHP code?

$fruits = ['apple', 'banana', 'cherry'];
echo count($fruits);

medium

A. 0

B. 3

C. applebanana cherry

D. Error

Solution

1. Step 1: Identify the array elements

   The array $fruits contains three elements: 'apple', 'banana', and 'cherry'.

2. Step 2: Apply count() function

   The count() function returns the number of elements, which is 3.

3. Final Answer:

   3 -> Option B

4. Quick Check:

   count(['apple','banana','cherry']) = 3 [OK]

Hint: Count returns number of items, not their values. [OK]

Common Mistakes:

• Expecting count() to print array contents
• Confusing count() with string concatenation
• Thinking count() returns 0 for non-empty arrays

4. Consider this PHP code snippet:

$numbers = [1, 2, 3, 4];
$count = count($numbers
echo $count;

What is the problem with this code?

medium

A. Missing semicolon after count() function call.

B. count() cannot be used on numeric arrays.

C. Missing closing parenthesis in count() function call.

D. Variable $count is not defined before use.

Solution

1. Step 1: Check syntax of count() call

   The code count($numbers is missing a closing parenthesis ")".

2. Step 2: Verify other syntax elements

   There is no semicolon after the count() call, but the bigger issue is the missing parenthesis which causes a syntax error first.

3. Final Answer:

   Missing closing parenthesis in count() function call. -> Option C

4. Quick Check:

   count() needs matching parentheses [OK]

Hint: Always check parentheses balance in function calls. [OK]

Common Mistakes:

• Ignoring missing parenthesis and blaming semicolon
• Thinking count() can't be used on numeric arrays
• Assuming variable must be declared before assignment

5. You have an associative array in PHP:

$person = ['name' => 'Alice', 'age' => 30, 'city' => 'Paris'];

Which code correctly checks if the array has exactly 3 elements before printing "Valid"?

hard

A. if (count($person) == 3) { echo "Valid"; }

B. if (sizeof($person) > 3) { echo "Valid"; }

C. if (count($person) < 3) { echo "Valid"; }

D. if (length($person) == 3) { echo "Valid"; }

Solution

1. Step 1: Understand the array and count() usage

   The array $person has 3 key-value pairs. Using count() returns the number of elements.

2. Step 2: Check the condition for exactly 3 elements

   if (count($person) == 3) { echo "Valid"; } correctly uses count($person) == 3 to check if the array has exactly 3 elements.

3. Final Answer:

   if (count($person) == 3) { echo "Valid"; } -> Option A

4. Quick Check:

   count() == 3 means array has 3 elements [OK]

Hint: Use count() == number to check exact array size. [OK]

Common Mistakes:

• Using sizeof() with wrong comparison operator
• Using length() which is not a PHP function
• Checking for less or greater instead of exact count