🧩 C++ Tokens – The Smallest Building Blocks of C++ Code

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🧲 Introduction – What Are Tokens in C++?

In C++, a token is the smallest meaningful unit in the source code. Just as sentences are made of words, a C++ program is made of tokens. Understanding tokens is essential because they define how code is broken down and interpreted by the compiler.

🎯 In this guide, you’ll learn:

• What tokens are in C++
• The 6 types of tokens with examples
• Role of each token during compilation
• Common errors caused by incorrect token usage

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🧩 What Is a Token?

A token is a lexical unit or smallest element recognized by the compiler during lexical analysis (first stage of compilation).

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🧱 Types of Tokens in C++

C++ supports six major types of tokens:

🔢 Token Type	🔍 Description	💡 Example
1️⃣ Keywords	Reserved words with special meaning	int, while, class
2️⃣ Identifiers	Names of variables, functions, arrays, etc.	main, sum, myVar
3️⃣ Literals	Constant values that do not change	10, 'A', "Hello"
4️⃣ Operators	Symbols that perform operations	+, -, *, ==
5️⃣ Punctuation / Separators	Characters that structure the code	;, {}, (), ,
6️⃣ Comments	Non-executable, ignored by compiler	// single line, /* ... */

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🔑 1. Keywords (Reserved Words)

These are predefined words in C++ with fixed meanings.

int main() {
    return 0;
}

✅ Examples: int, return, while, if, else, class, public, private

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🆔 2. Identifiers

Identifiers are user-defined names for:

• Variables
• Functions
• Classes
• Arrays, etc.

int age;
float calculateArea(float radius);

✅ Must start with a letter or underscore
❌ Cannot use C++ keywords as identifiers

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🔢 3. Literals (Constants)

Literals are fixed values assigned to variables.

int x = 100;       // Integer literal
char grade = 'A';  // Character literal
string name = "Alex"; // String literal

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➕ 4. Operators

Used to perform operations on variables and values.

int sum = a + b;

Types of operators:

• Arithmetic (+, -, *, /)
• Relational (==, !=, <, >)
• Logical (&&, ||, !)
• Assignment (=, +=, -=)
• Bitwise (&, |, ~, ^)
• Unary (++, --)
• Ternary (?:)

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🔗 5. Separators / Punctuation

Help in grouping and separating elements of the program.

int main() {
    cout << "Hello!";
    return 0;
}

Examples:

• Semicolon ;
• Comma ,
• Parentheses ()
• Curly braces {}
• Square brackets []

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💬 6. Comments (Ignored Tokens)

Comments are part of tokens but not part of the compiled output.

// This is a single-line comment
/* This is a 
   multi-line comment */

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🔍 Example – Token Breakdown

int age = 25;  // Declare an integer variable

Token breakdown:

• int → Keyword
• age → Identifier
• = → Operator
• 25 → Literal
• ; → Separator
• // ... → Comment

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⚠️ Common Mistakes with Tokens

❌ Mistake	✅ Fix
Using keywords as identifiers	Avoid names like int, while, return
Missing semicolon	Every statement must end with ;
Illegal characters in identifiers	Use only letters, digits, and underscore
Nested or broken comments	Don’t nest /* */ comments in C++

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📌 Summary – Recap & Next Steps

🔍 Key Takeaways:

• Tokens are the smallest building blocks of C++ code
• There are six types: keywords, identifiers, literals, operators, separators, and comments
• Proper token usage is essential for writing correct, compilable programs

⚙️ Real-World Relevance:
Understanding tokens helps you write syntactically correct code and avoid compiler-level issues early in development.

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❓ FAQs – C++ Tokens

❓ What is a token in C++?
✅ A token is a smallest meaningful unit in the source code such as a keyword, identifier, literal, etc.

❓ Can I use C++ keywords as variable names?
❌ No. They are reserved by the language and will result in a compilation error.

❓ Are comments considered tokens?
✅ Yes, during lexical analysis, comments are treated as tokens but ignored in later compilation stages.

❓ How do I fix a “missing semicolon” error?
✅ Check that each statement ends with ; – it’s a required separator in C++.

❓ Can tokens be reused across files?
✅ Identifiers can be reused via functions or variable definitions if properly scoped.

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