Constant

Definition

A constant is a value that remains unchanged throughout the execution of a program or the evaluation of an expression. In programming languages, constants can be of various types, such as integers, floating-point numbers, characters, and strings. Literal expressions such as 3.5 (a floating-point constant) and "George Washington" (a string constant) are constants because they refer to a fixed value.

Examples

Mathematical Constant:
```
1PI = 3.14159
```
String Constant:
```
1GREETING = "Hello, World!"
```
Integer Constant:
```
1MAX_USERS = 100
```

Frequently Asked Questions (FAQs)

What is the difference between a constant and a variable?

Constant: A value that does not change throughout the program execution.
Variable: A value that may change during the program execution.

Can constants be reassigned after their initial definition?

No, constants cannot be reassigned to hold a different value once they have been defined. If reassignment is attempted, it will typically result in an error.

Are there different types of constants?

Yes, constants can be:

Numeric Constants: Such as 42 or 3.14.
Character Constants: Such as 'A'.
String Constants: Such as "Hello".

How are constants defined in various programming languages?

The syntax varies by language. For example:

Python: PI = 3.14159
C/C++: const float PI = 3.14159;
JavaScript: const PI = 3.14159;

Why are constants important in programming?

Constants enhance code readability and maintainability by providing clear and unchangeable references to fixed values.

Variable

A storage location paired with an associated symbolic name that contains some known or unknown quantity of information referred to as a value.

Literal

A notation for representing a fixed value in source code.

Constant Expression

An expression that can always be evaluated at compile time and consistently produces the same value.

Online References

Suggested Books for Further Study

“Clean Code: A Handbook of Agile Software Craftsmanship” by Robert C. Martin
“The Pragmatic Programmer” by Andrew Hunt and David Thomas
“Python Programming: An Introduction to Computer Science” by John M. Zelle
“JavaScript: The Good Parts” by Douglas Crockford

Fundamentals of Constants: Computer Science Basics Quiz

### What is a constant in programming? - [ ] A value that can change during execution - [x] A value that remains unchanged during execution - [ ] A keyword in the programming language - [ ] A type of variable > **Explanation:** A constant is a value that remains unchanged during the execution of a program. ### Which of the following is a constant? - [x] 3.14 - [ ] num - [ ] variable - [ ] function() > **Explanation:** `3.14` is a numeric constant that does not change. ### Can a constant be reassigned a value after initial declaration? - [ ] Yes - [x] No > **Explanation:** No, once a constant is defined, it cannot be reassigned a different value. ### How is a constant defined in Python? - [ ] `let PI = 3.14` - [ ] `dim PI as 3.14` - [x] `PI = 3.14` - [ ] `const PI` > **Explanation:** In Python, constants are typically defined using good naming conventions (all uppercase letters) despite not having built-in keyword support for constants similar to other languages. ### What keyword is used in JavaScript to define a constant? - [ ] var - [ ] let - [x] const - [ ] int > **Explanation:** In JavaScript, the `const` keyword is used to define a constant. ### Why are constants valuable in programming? - [ ] To allow value changes during execution - [ ] To store temporary information - [x] To enhance code readability and maintainability - [ ] To hold large volumes of information > **Explanation:** Constants enhance code readability and maintainability because their fixed values make the code easier to understand and manage. ### Which of the following is NOT a type of constant? - [ ] Numeric - [ ] String - [ ] Boolean - [x] Variable > **Explanation:** A variable can change its value during execution, making it different from constants. ### How would you define a constant in C/C++? - [x] `const float PI = 3.14;` - [ ] `float PI == 3.14;` - [ ] `PI = constant float = 3.14;` - [ ] `let PI equal 3.14;` > **Explanation:** In C/C++, constants are defined using the `const` keyword followed by a data type and the assigned value. ### Can constants be used for array sizes in C++? - [x] Yes - [ ] No > **Explanation:** Constants in C++ can be used to define array sizes as fixed dimensions, ensuring array size remains unchanged. ### Which of the following literals is considered a string constant? - [ ] `126` - [ ] `3.14` - [x] `"Hello, World!"` - [ ] `'A'` > **Explanation:** `"Hello, World!"` is a string constant, because it consists of a sequence of characters enclosed in double quotes.

Thank you for exploring the concept of constants with us. Keep delving into programming concepts to solidify your understanding and enhance your coding skills!