🔒 C++ Constants and Literals – Fixed Values in Your Code

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🧲 Introduction – What Are Constants and Literals in C++?

In C++, constants and literals represent fixed values that do not change during program execution. Constants are often used to make code more readable, maintainable, and secure by preventing accidental changes to important values.

🎯 In this guide, you’ll learn:

• What constants and literals are
• Types of literals in C++
• How to define and use constants
• Key differences between const, #define, and literals

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🔐 What Are Constants in C++?

A constant is a named value that cannot be modified after its declaration.

✅ Declaring Constants Using const Keyword

const float PI = 3.14159;
const int MAX_USERS = 100;

• Cannot be changed after initialization
• Must be initialized during declaration

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🧮 What Are Literals?

A literal is a fixed value used directly in the code. It can represent:

• Numbers (42)
• Characters ('A')
• Strings ("Hello")
• Boolean values (true, false)

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🔢 Types of Literals in C++

1️⃣ Integer Literals

int num = 100;
int hex = 0xFF;     // Hexadecimal
int bin = 0b1010;   // Binary (C++14+)

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2️⃣ Floating-point Literals

float pi = 3.14f;
double gravity = 9.8;

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3️⃣ Character Literals

char grade = 'A';
char newline = '\n';

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4️⃣ String Literals

string message = "Welcome!";

⚠️ In C++, string literals like "Hello" are of type const char[].

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5️⃣ Boolean Literals

bool isOnline = true;
bool isDead = false;

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6️⃣ Null Pointer Literal (C++11)

int* ptr = nullptr;   // Preferred over NULL

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✏️ Example – Constants & Literals Together

#include <iostream>
using namespace std;

int main() {
    const float TAX_RATE = 0.18;   // Constant
    float price = 100.0;           // Literal 100.0
    float tax = price * TAX_RATE;

    cout << "Tax: " << tax << endl;
    return 0;
}

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🆚 const vs #define for Constants

Feature	const	#define
Type-safe	✅ Yes	❌ No
Scoped	✅ Respects C++ scoping rules	❌ Global by default
Debuggable	✅ Better error messages	❌ No type info during debugging
Preferred in C++	✅ Use const, constexpr, enum	❌ Legacy C macro usage

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📌 Summary – Recap & Next Steps

🔍 Key Takeaways:

• Constants are fixed variables defined using const or constexpr
• Literals are fixed values like 42, 'A', 3.14, or "text"
• Prefer const over #define for type safety and maintainability

⚙️ Real-World Relevance:
Using constants and literals correctly reduces hard-coded values, improves code clarity, and prevents bugs from accidental value changes.

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❓ FAQs – C++ Constants and Literals

❓ What is the difference between a constant and a literal?
✅ A constant is a named value (const int max = 10;), while a literal is a raw value (10).

❓ Can I change a const value later?
❌ No. Once declared, a const variable cannot be modified.

❓ Should I use #define or const in C++?
✅ Use const or constexpr—they are type-safe and scoped.

❓ What is a string literal?
✅ A string value enclosed in double quotes, e.g., "Hello".

❓ What is nullptr?
✅ It is a C++11 keyword representing a null pointer value, preferred over NULL.

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