Array count and length in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of count() with nested arrays

What is the output of the following PHP code?

PHP

<?php
$array = [1, 2, [3, 4], 5];
echo count($array);
?>

A 3

B 5

C Error

D 4

💡 Hint

count() counts the top-level elements only.

The array has four elements: 1, 2, [3,4], and 5. The nested array counts as one element.

❓ Predict Output

intermediate

Difference between count() and sizeof()

What will this PHP code output?

PHP

<?php
$arr = ['a', 'b', 'c'];
echo count($arr) . ' ' . sizeof($arr);
?>

A 3 0

B 0 3

C 3 3

D Error

💡 Hint

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

Both count() and sizeof() return the number of elements in the array, which is 3.

❓ Predict Output

advanced

Count with COUNT_RECURSIVE flag

What is the output of this PHP code?

PHP

<?php
$array = [1, 2, [3, 4], 5];
echo count($array, COUNT_RECURSIVE);
?>

A 4

B 6

C 5

D Error

💡 Hint

COUNT_RECURSIVE counts all elements including nested arrays.

The array has 4 top-level elements, but the nested array has 2 elements, so total is 4 + 2 = 6.

❓ Predict Output

advanced

Length of string vs count() on string

What will this PHP code output?

PHP

<?php
$str = "hello";
echo count($str);
?>

A 1

B 5

C Error

D 0

💡 Hint

count() on a string returns 1 because string is not an array.

count() returns 1 when given a non-array, non-countable variable like a string.

🧠 Conceptual

expert

Why does count() return 1 on a string?

In PHP, why does count() return 1 when called on a string variable?

A Because count() treats any non-array as a single element

B Because strings are internally arrays of characters

C Because count() counts characters in the string

D Because count() throws an error on strings

💡 Hint

Think about how count() handles non-array inputs.

count() returns 1 for any scalar (non-array) value, treating it as a single element.

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