C++ Constants

In C++, a constant is a value that cannot be changed during the execution of a program. Once a constant is defined, its value remains the same throughout the program.

Using the const Keyword

The const keyword is used to declare constant variables.

const int age = 25;

In this example, the value of age cannot be changed after it is defined.

Example Program

#include <iostream>
using namespace std;

int main() {

    const float PI = 3.14159;

    cout << "Value of PI: " << PI;

    return 0;
}

Output

Value of PI: 3.14159

Using #define for Constants

Constants can also be defined using the #define preprocessor directive.

#define PI 3.14159

This method defines a constant value before the program is compiled.

Example Using #define

#include <iostream>
using namespace std;

#define PI 3.14159

int main() {

    cout << "Value of PI: " << PI;

    return 0;
}

Rules for Constants

The value of a constant cannot be changed after declaration.
Constants must be initialized when they are declared.
Constant names are usually written in uppercase to distinguish them from variables.

Advantages of Constants

Improves code readability.
Prevents accidental modification of important values.
Makes programs easier to maintain.

Next Topic

Next, learn about C++ Operators.