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.

Practice

1. What does the PHP function strlen() do?

easy

A. It removes spaces from a string.

B. It converts a string to uppercase.

C. It splits a string into an array.

D. It returns the number of characters in a string.

Solution

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

   The strlen() function counts all characters in a string, including letters, spaces, and symbols.

2. Step 2: Compare with other options

   Other options describe different string functions, not strlen().

3. Final Answer:

   It returns the number of characters in a string. -> Option D

4. Quick Check:

   strlen() counts characters [OK]

Hint: Remember: strlen() counts all characters in a string [OK]

Common Mistakes:

• Thinking strlen() changes the string
• Confusing strlen() with string splitting
• Assuming it removes spaces

2. Which of the following is the correct syntax to get the length of a string stored in variable $text?

easy

A. strlen($text);

B. size($text);

C. count($text);

D. length($text);

Solution

1. Step 1: Identify the correct function for string length

   In PHP, strlen() is the built-in function to get string length.

2. Step 2: Check syntax correctness

   strlen($text); correctly calls the function with the variable.

3. Final Answer:

   strlen($text); -> Option A

4. Quick Check:

   Use strlen() with parentheses and variable [OK]

Hint: Use strlen() with parentheses around the variable [OK]

Common Mistakes:

• Using length() which is not a PHP function
• Using count() which is for arrays
• Forgetting parentheses

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

$str = "Hello World!";
echo strlen($str);

medium

A. 12

B. 10

C. 11

D. 13

Solution

1. Step 1: Count characters in the string including spaces and punctuation

   The string "Hello World!" has 12 characters: 5 letters + 1 space + 5 letters + 1 exclamation mark.

2. Step 2: Confirm strlen() counts all characters

   strlen($str) returns 12 because it counts every character.

3. Final Answer:

   12 -> Option A

4. Quick Check:

   Count all characters including spaces and punctuation [OK]

Hint: Count every character including spaces and symbols [OK]

Common Mistakes:

• Ignoring spaces in count
• Forgetting punctuation counts
• Assuming strlen() excludes special characters

4. Identify the error in the following PHP code that tries to print the length of a string:

$text = "PHP Rocks!";
echo strlen $text;

medium

A. Missing semicolon after echo

B. strlen() function call missing parentheses

C. Variable name is incorrect

D. String is not enclosed in quotes

Solution

1. Step 1: Check function call syntax

   In PHP, functions require parentheses around their arguments. Here, strlen is called without parentheses.

2. Step 2: Verify other parts of the code

   The variable name and string are correct, and semicolon is present after echo statement.

3. Final Answer:

   strlen() function call missing parentheses -> Option B

4. Quick Check:

   Always use parentheses when calling functions [OK]

Hint: Functions need parentheses even with one argument [OK]

Common Mistakes:

• Omitting parentheses in function calls
• Confusing variable names
• Missing semicolon after statements

5. You want to check if a user's input stored in $input is exactly 8 characters long. Which PHP code correctly performs this check?

hard

A. if (strlen($input) > 8) { echo "Valid length"; } else { echo "Invalid length"; }

B. if (count($input) == 8) { echo "Valid length"; } else { echo "Invalid length"; }

C. if (strlen($input) == 8) { echo "Valid length"; } else { echo "Invalid length"; }

D. if (strlen($input) != 8) { echo "Valid length"; } else { echo "Invalid length"; }

Solution

1. Step 1: Use strlen() to get string length

   The function strlen($input) returns the number of characters in the input string.

2. Step 2: Compare length to 8 exactly

   The condition strlen($input) == 8 checks if the length is exactly 8 characters.

3. Step 3: Understand other options

   if (count($input) == 8) { echo "Valid length"; } else { echo "Invalid length"; } uses count() which is for arrays, not strings. if (strlen($input) > 8) { echo "Valid length"; } else { echo "Invalid length"; } checks if length is greater than 8, not equal. if (strlen($input) != 8) { echo "Valid length"; } else { echo "Invalid length"; } reverses logic.

4. Final Answer:

   if (strlen($input) == 8) { echo "Valid length"; } else { echo "Invalid length"; } -> Option C

5. Quick Check:

   Use strlen() == 8 to check exact length [OK]

Hint: Use strlen() == 8 to check exact string length [OK]

Common Mistakes:

• Using count() on strings
• Using > or != instead of == for exact match
• Confusing string length with array size