Case conversion functions in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of strtolower and strtoupper

What is the output of this PHP code?

PHP

<?php
$text = "Hello World!";
echo strtolower($text) . " - " . strtoupper($text);
?>

A hello world! - HELLO WORLD!

B HELLO WORLD! - hello world!

C Hello World! - Hello World!

D hello world! - hello world!

💡 Hint

strtolower converts all letters to lowercase, strtoupper converts all letters to uppercase.

The function strtolower converts all characters in the string to lowercase, and strtoupper converts all characters to uppercase. So the output is the lowercase version, then a dash, then the uppercase version.

❓ Predict Output

intermediate

Output of ucfirst and lcfirst

What is the output of this PHP code?

PHP

<?php
$text = "hello WORLD!";
echo ucfirst($text) . " - " . lcfirst(strtoupper($text));
?>

A Hello WORLD! - Hello WORLD!

B hello WORLD! - Hello WORLD!

C Hello WORLD! - hELLO WORLD!

D hello WORLD! - hELLO world!

💡 Hint

ucfirst makes first letter uppercase, lcfirst makes first letter lowercase.

ucfirst makes the first character uppercase and leaves the rest unchanged. strtoupper converts all letters to uppercase, then lcfirst makes the first letter lowercase again.

❓ Predict Output

advanced

Output of mb_convert_case with mixed UTF-8 string

What is the output of this PHP code using mb_convert_case with UTF-8 encoding?

PHP

<?php
$text = "mÜnchEn ist schön";
echo mb_convert_case($text, MB_CASE_TITLE, "UTF-8");
?>

A mÜnchEn ist schön

B München Ist Schön

C MÜNCHEN IST SCHÖN

D MünchEn Ist Schön

💡 Hint

MB_CASE_TITLE capitalizes the first letter of each word correctly for UTF-8 strings.

mb_convert_case with MB_CASE_TITLE converts the first character of each word to uppercase and the rest to lowercase, respecting UTF-8 characters like Ü and ö.

❓ Predict Output

advanced

Output of strcasecmp function

What is the output of this PHP code?

PHP

<?php
$a = "Hello";
$b = "hello";
$result = strcasecmp($a, $b);
echo $result > 0 ? "A" : ($result < 0 ? "B" : "C");
?>

A A

B Error

C B

D C

💡 Hint

strcasecmp compares strings ignoring case and returns 0 if equal.

strcasecmp compares two strings case-insensitively. Since "Hello" and "hello" are equal ignoring case, it returns 0, so the output is "C".

🧠 Conceptual

expert

Why use mb_strtolower over strtolower?

Why should you use mb_strtolower instead of strtolower when working with UTF-8 strings in PHP?

A mb_strtolower correctly converts multibyte UTF-8 characters to lowercase, while strtolower only works reliably with ASCII characters.

B mb_strtolower is faster than strtolower for all strings.

C strtolower converts strings to uppercase, mb_strtolower converts to lowercase.

D mb_strtolower only works with ASCII, strtolower works with UTF-8.

💡 Hint

Think about characters like accented letters or non-English alphabets.

strtolower only handles single-byte ASCII characters correctly. For UTF-8 strings with multibyte characters (like accented letters), mb_strtolower is needed to convert them properly to lowercase.

Practice

1. Which PHP function converts all letters in a string to uppercase?
$text = "hello world";

easy

A. strtoupper()

B. strtolower()

C. ucfirst()

D. ucwords()

Solution

1. Step 1: Understand the function purpose

   strtoupper() converts all characters in a string to uppercase letters.

2. Step 2: Compare with other functions

   strtolower() makes all letters lowercase, ucfirst() capitalizes only the first letter, and ucwords() capitalizes the first letter of each word.

3. Final Answer:

   strtoupper() -> Option A

4. Quick Check:

   Uppercase function = strtoupper() [OK]

Hint: All uppercase letters? Use strtoupper() [OK]

Common Mistakes:

• Confusing strtoupper() with strtolower()
• Using ucfirst() to uppercase whole string
• Using ucwords() for full uppercase

2. Which of the following is the correct syntax to convert a string to lowercase in PHP?
$str = "HELLO";

easy

A. strtolower->$str();

B. strtolower $str;

C. strtolower($str);

D. strtolower{$str};

Solution

1. Step 1: Identify correct function call syntax

   In PHP, functions are called with parentheses enclosing arguments, like functionName(argument);.

2. Step 2: Check each option

   strtolower($str); uses correct syntax: strtolower($str);. Others have syntax errors or invalid usage.

3. Final Answer:

   strtolower($str); -> Option C

4. Quick Check:

   Function call syntax = strtolower($str); [OK]

Hint: Function calls need parentheses around arguments [OK]

Common Mistakes:

• Missing parentheses in function call
• Using arrow or braces incorrectly
• Confusing function call with variable access

3. What is the output of the following PHP code?

$name = "john doe";
echo ucfirst($name);

medium

A. John doe

B. john Doe

C. JOHN DOE

D. john doe

Solution

1. Step 1: Understand ucfirst() behavior

   ucfirst() capitalizes only the first character of the entire string, leaving the rest unchanged.

2. Step 2: Apply to given string

   Input is "john doe". After ucfirst(), it becomes "John doe" (only first letter capitalized).

3. Final Answer:

   John doe -> Option A

4. Quick Check:

   ucfirst("john doe") = "John doe" [OK]

Hint: ucfirst() capitalizes only first letter of whole string [OK]

Common Mistakes:

• Expecting all words capitalized
• Confusing ucfirst() with ucwords()
• Assuming it converts whole string to uppercase

4. The following PHP code is intended to capitalize the first letter of each word in a string, but it does not work as expected:

$text = "hello world";
echo ucfirst($text);

What is the correct fix?

medium

A. Replace ucfirst() with strtoupper()

B. Replace ucfirst() with ucwords()

C. Replace ucfirst() with strtolower()

D. No fix needed, code is correct

Solution

1. Step 1: Identify function behavior

   ucfirst() capitalizes only the first letter of the entire string, not each word.

2. Step 2: Choose function to capitalize each word

   ucwords() capitalizes the first letter of every word in the string.

3. Final Answer:

   Replace ucfirst() with ucwords() -> Option B

4. Quick Check:

   Capitalize each word = ucwords() [OK]

Hint: Use ucwords() to capitalize first letter of each word [OK]

Common Mistakes:

• Using ucfirst() instead of ucwords()
• Using strtoupper() which uppercases all letters
• Thinking code is already correct

5. You have a string with mixed case: $input = "hElLo WoRLd";. You want to convert it so that only the first letter of each word is uppercase and the rest are lowercase. Which PHP code achieves this?

hard

A. $output = ucfirst(strtolower($input));

B. $output = strtoupper(ucwords($input));

C. $output = strtolower(ucfirst($input));

D. $output = ucwords(strtolower($input));

Solution

1. Step 1: Normalize string to lowercase

   Use strtolower() to convert all letters to lowercase first, so mixed case is fixed.

2. Step 2: Capitalize first letter of each word

   Apply ucwords() to capitalize the first letter of every word in the now lowercase string.

3. Final Answer:

   $output = ucwords(strtolower($input)); -> Option D

4. Quick Check:

   Lowercase then ucwords() = desired format [OK]

Hint: Lowercase first, then ucwords() for title case [OK]

Common Mistakes:

• Applying ucwords() before strtolower()
• Using strtoupper() which uppercases all letters
• Using ucfirst() which only capitalizes first letter of string