🔑 C++ Keywords – Reserved Words Every Programmer Must Know

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🧲 Introduction – What Are Keywords in C++?

Keywords in C++ are reserved words that have special meaning to the compiler. These words are part of the C++ language syntax and cannot be used as names for variables, functions, classes, or identifiers. They play a fundamental role in defining the structure and behavior of C++ programs.

🎯 In this guide, you’ll learn:

• What keywords are and why they matter
• The full list of C++ keywords (updated for C++23)
• How keywords are used in actual programs
• Common beginner mistakes to avoid

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📘 What Is a Keyword in C++?

A keyword is a built-in command or symbol that tells the C++ compiler to perform a specific task or recognize a syntactic construct.

int main() {
    return 0;
}

In the code above:

• int and return are keywords
• main is an identifier, not a keyword

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🧾 List of C++ Keywords (Including C++11 – C++23)

🔹 Category	🔑 Keywords
Data Types	int, char, float, double, bool, void, wchar_t
Control Statements	if, else, switch, case, default, break, continue, goto, do, while, for
Modifiers	const, static, mutable, volatile, register, extern, inline
Classes/OOP	class, struct, union, enum, public, private, protected, virtual, friend, this, new, delete
Functions	return, try, catch, throw, noexcept, explicit, operator, override, final
Templates	template, typename, using, namespace
Boolean & Null	true, false, nullptr
Type Operators	sizeof, typeid, decltype, alignof
Coroutines (C++20)	co_await, co_yield, co_return
Modern C++	constexpr, consteval, constinit, concept, requires, static_assert, import, module

✅ Total: Over 95 keywords, updated with each standard release.

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🧪 Example – Keywords in Use

#include <iostream>

int main() {
    const int maxMarks = 100;   // const is a keyword
    int score = 85;

    if (score < maxMarks) {
        std::cout << "You passed!" << std::endl;
    }
    return 0;
}

🔍 In this example:

• int, const, if, and return are keywords.
• main, maxMarks, and score are identifiers.

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⚠️ Common Mistakes with Keywords

❌ Mistake	✅ Correction
Using a keyword as a variable	int int = 5; → ❌ Illegal
Typing keyword in uppercase	Return ≠ return (C++ is case-sensitive)
Assuming main is a keyword	main is not a keyword—it’s a special name
Trying to redefine keywords	Cannot define int or class as identifiers

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📌 Summary – Recap & Next Steps

🔍 Key Takeaways:

• Keywords are reserved words with predefined purposes in C++
• You cannot use them as names for variables or functions
• Learn and recognize all standard keywords, especially as C++ evolves
• Understanding keyword usage is essential for valid program syntax

⚙️ Real-World Relevance:
A deep understanding of keywords helps prevent syntax errors, improves code readability, and ensures that your programs follow modern C++ standards.

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❓ FAQs – C++ Keywords

❓ Are C++ keywords case-sensitive?
✅ Yes. int is valid, but Int is treated as an identifier.

❓ Can I use keywords as variable names?
❌ No. Keywords are reserved and cannot be redefined or reused.

❓ Is main a keyword?
❌ No. It’s a special function name, not a keyword.

❓ What are new keywords in C++20 and C++23?
✅ Examples include concept, requires, consteval, co_await, and module.

❓ How many keywords are there in modern C++?
✅ Over 95 keywords, with additions in every major C++ standard.

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