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Constants in C++

What is Constants in C++?​

Constants in C++ are fixed values that cannot be altered during the execution of a program. They are used to define values that should remain unchanged throughout the program, providing a way to ensure data integrity and improving code readability.

IMAGE FILE: Constants in CPP

How to Declare Constants in C++?​

Constants can be declared in C++ using the const keyword. The const keyword is placed before the data type of the variable to indicate that its value will not change.

Example:​

const int DAYS_IN_WEEK = 7;
const float PI = 3.14159;

How to Define Constants in C++?​

Constants are defined at the time of declaration by assigning them a fixed value. Once defined, their value cannot be modified.

Example:​

const double GRAVITY = 9.81; // gravitational constant in m/s^2
const char NEWLINE = '\n'; // newline character

How to Use Constants in C++?​

Constants are used just like regular variables in expressions, function calls, and other places where a variable would be used. The key difference is that their value remains unchanged.

Example​

const int MAX_USERS = 100;

int main() {
    int users = MAX_USERS;
    std::cout << "Maximum number of users: " << users << std::endl;
    return 0;
}

What are the Advantages of Constants in C++?​

  • Readability: Constants make the code more readable by giving meaningful names to fixed values.
  • Maintainability: Constants allow easy modification of values without changing multiple instances in the code.
  • Safety: Constants prevent accidental modification of values that should remain fixed, reducing bugs and errors.
  • Optimization: Constants can sometimes allow the compiler to optimize the code better since their values are known at compile time.

Best Practices for Using Constants in C++:​

  • Use Descriptive Names: Choose names that clearly describe the value or purpose of the constant.
  • All Uppercase with Underscores: Use all uppercase letters with underscores to separate words for naming constants, making them easily distinguishable from variables.
  • Define Constants at the Top: Define all constants at the beginning of the file or in a dedicated section for easy reference and modification.
  • Group Related Constants: Group related constants together to improve code organization.
  • Use constexpr for Compile-Time Constants: Use constexpr when the constant value can be determined at compile time for better performance.

Example:​

constexpr int ARRAY_SIZE = 50;
const double SPEED_OF_LIGHT = 299792458.0; // in meters per second

Examples of Constants in C++​

#include <iostream>

const int MAX_AGE = 120;
constexpr double PLANCK_CONSTANT = 6.62607015e-34;

int main() {
    const char GRADE = 'A';
    const std::string SCHOOL_NAME = "Greenwood High";

    std::cout << "Max age allowed: " << MAX_AGE << std::endl;
    std::cout << "Planck constant: " << PLANCK_CONSTANT << std::endl;
    std::cout << "Grade: " << GRADE << std::endl;
    std::cout << "School name: " << SCHOOL_NAME << std::endl;

    return 0;
}