C++ Programs Const Keyword

In C++, the const keyword is used to indicate that a value is a constant and cannot be modified. Constants are useful when you want to define a value that should not change throughout the program execution.

Syntax

const data_type variable_name = value;

In the above syntax, data_type can be any valid C++ data type, and variable_name can be any valid C++ identifier. The value of a constant variable cannot be changed once it is declared.

Example

#include <iostream>
using namespace std;

int main() {
    const int x = 10; // declare constant variable
    // x = 20; // this line will cause a compilation error
    cout << x << endl;
    return 0;
}

Output

10

Explanation

In the above example, we have declared a constant variable x and assigned it the value 10. Since x is a constant, we cannot change its value in the program. If we try to modify the value of x, the program will fail to compile.

Use

Constants are used in C++ programs to define values that do not need to be changed during program execution. They are especially useful when you need to define a fixed value that multiple parts of your program can reference.

#include <iostream>
using namespace std;

const float PI = 3.14159;

float circle_area(float radius) {
    return PI * radius * radius;
}

int main() {
    float r = 5;
    float area = circle_area(r);
    cout << "The area of the circle is: " << area << endl;
    return 0;
}

In the above example, we have defined a constant PI and used it in a function to calculate the area of a circle. The value of PI is fixed and will not change during program execution.

Important Points

• Constants are values that cannot be changed during program execution
• The const keyword is used to declare a constant variable
• The value of a constant variable cannot be changed after it is declared
• Constants can be used to define fixed values that multiple parts of the program can reference

Summary

In summary, the const keyword is used in C++ programs to define constant values that cannot be changed during program execution. Constants are useful when you need to define a fixed value that multiple parts of your program can reference.