🟢 Basic Level (Very Important)

1️⃣ What is a string in PHP?
2️⃣ What are the different ways to define a string in PHP?
3️⃣ Difference between single quotes (‘ ‘) and double quotes (” “)?
4️⃣ What is string concatenation? How is it done in PHP?
5️⃣ What does strlen() do?
6️⃣ What is the use of strpos()?
7️⃣ How to convert a string to uppercase/lowercase in PHP?
8️⃣ What is trim()? Why is it used?

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🟡 Intermediate Level

9️⃣ What is the difference between:

• echo and print for strings?

🔟 Explain substr() with an example.

1️⃣1️⃣ How to replace a word inside a string?

1️⃣2️⃣ What is the difference between:

• str_replace() and substr_replace()?

1️⃣3️⃣ How to check if a substring exists in a string?

1️⃣4️⃣ What is strcmp()?

1️⃣5️⃣ How can you count occurrences of a substring?

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🟠 explode() / implode() (Very Common in Interviews)

1️⃣6️⃣ What does explode() do?
1️⃣7️⃣ What does implode() do?
1️⃣8️⃣ Difference between explode() and str_split()?
1️⃣9️⃣ Give a real-world use case of explode().

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🔵 Advanced String Concepts

2️⃣0️⃣ What is a mutable vs immutable string? (PHP context)

2️⃣1️⃣ What is the difference between:

• == and === in string comparison?

2️⃣2️⃣ What is string interpolation?

2️⃣3️⃣ What are heredoc and nowdoc in PHP?

2️⃣4️⃣ How does PHP handle special characters in strings?

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🔴 Regex (Highly Important)

2️⃣5️⃣ What is Regular Expression (Regex)?

2️⃣6️⃣ What is preg_match()?

2️⃣7️⃣ Difference between:

• preg_match() and preg_match_all()?

2️⃣8️⃣ What is preg_replace()?

2️⃣9️⃣ Write a regex to validate:

• Email
• Only numbers
• Only alphabets

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🟣 Scenario-Based Questions (Asked in Real Interviews)

3️⃣0️⃣ How would you validate a user input string?

3️⃣1️⃣ How to remove HTML tags from a string?

3️⃣2️⃣ How to generate a URL-friendly string (slug)?

3️⃣3️⃣ How to check if a string is a palindrome?

3️⃣4️⃣ How to mask sensitive data (email/phone)?

3️⃣5️⃣ How to extract all numbers from a string?

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🧠 Coding Questions (Must Practice)

3️⃣6️⃣ Reverse a string without using strrev()

3️⃣7️⃣ Count vowels in a string

3️⃣8️⃣ Find the first non-repeating character

3️⃣9️⃣ Remove duplicate characters from a string

4️⃣0️⃣ Find the longest word in a sentence

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🎯 Pro Tips for Interviews

• Focus on functions + logic
• Practice real-world problems
• Be ready to write clean code on whiteboard
• Understand Regex basics (very important)