C++ Constants

📌 C++ Constants – Create Fixed Values in C++

Constants are like permanent stickers on your variables — once assigned, their value can’t change! 🔒

In C++, there are two common ways to define constants:

  • const keyword
  • #define preprocessor directive

🔍 Method 1: Using const

The const keyword is used to define a constant variable whose value cannot be changed later.

#include <iostream>
using namespace std;

int main() {
    const int DAYS_IN_WEEK = 7;

    cout << "There are " << DAYS_IN_WEEK << " days in a week." << endl;

    // DAYS_IN_WEEK = 8; // ❌ This will cause a compile-time error

    return 0;
}

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⚙️ Method 2: Using #define

#define is a preprocessor macro used to define constants before compilation begins.

#include <iostream>
#define PI 3.14159

using namespace std;

int main() {
    double radius = 5.0;
    double area = PI * radius * radius;

    cout << "Area of circle: " << area << endl;

    return 0;
}

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📘 Difference Between const and #define

  • const is type-safe and scoped (preferred in C++)
  • #define is a text replacement before compilation (older style)

🧠 Remember:

  • Use const for safer and modern C++ code
  • Constants make your code more readable and bug-resistant
  • Once a constant is defined, don’t even think about changing it! 😤