String length and counting in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of strlen with multibyte characters

What is the output of this PHP code?

$str = "café";
echo strlen($str);

PHP

$str = "café";
echo strlen($str);

A 3

B 4

C 6

D 5

💡 Hint

strlen counts bytes, not characters, in PHP.

The string "café" contains the character 'é' which is two bytes in UTF-8. So strlen returns 6 bytes total.

❓ Predict Output

intermediate

Counting occurrences of a character

What does this PHP code output?

$text = "hello world";
echo substr_count($text, "l");

PHP

$text = "hello world";
echo substr_count($text, "l");

A 4

B 2

C 1

D 3

💡 Hint

Count how many times 'l' appears in "hello world".

The letter 'l' appears 3 times in "hello world".

❓ Predict Output

advanced

Difference between strlen and mb_strlen

What is the output of this PHP code?

$str = "naïve";
echo strlen($str) . "," . mb_strlen($str);

PHP

$str = "naïve";
echo strlen($str) . "," . mb_strlen($str);

A 6,5

B 5,5

C 6,6

D 5,6

💡 Hint

strlen counts bytes, mb_strlen counts characters.

The character 'ï' is two bytes in UTF-8, so strlen returns 6 bytes, but mb_strlen returns 5 characters.

❓ Predict Output

advanced

Counting substring occurrences with overlapping

What is the output of this PHP code?

$text = "aaaaa";
echo substr_count($text, "aa");

PHP

$text = "aaaaa";
echo substr_count($text, "aa");

A 3

B 5

C 2

D 4

💡 Hint

substr_count does not count overlapping substrings.

The substring "aa" appears 3 times without overlapping: positions 0-1, 2-3, and 3-4.

🧠 Conceptual

expert

Why use mb_strlen over strlen?

Which statement best explains why mb_strlen is preferred over strlen for UTF-8 strings in PHP?

A mb_strlen is faster than strlen for all strings.

B mb_strlen counts the number of characters correctly in multibyte strings, while strlen counts bytes.

C strlen can only be used with ASCII strings, mb_strlen only with UTF-16 strings.

D strlen automatically converts strings to lowercase before counting.

💡 Hint

Think about how UTF-8 characters can use multiple bytes.

strlen counts bytes, so it can give wrong character counts for multibyte UTF-8 strings. mb_strlen counts characters correctly.