> For the complete documentation index, see [llms.txt](https://university-west.gitbook.io/programming-paradigms/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://university-west.gitbook.io/programming-paradigms/programming-fundamentals/variables-names.md).

# Constants and Variables

#### Constants and Variables in Computer Programming

In computer programming, constants and variables are two fundamental concepts used to store data. They serve as placeholders for values that can be used and manipulated throughout a program. However, they differ in how they are used and the flexibility they offer in storing and changing data.

**Variables**

* **Definition:** A variable is a storage location paired with an associated symbolic name (an identifier), which contains some known or unknown quantity of information referred to as a value.
* **Mutability:** The value stored in a variable can be changed during program execution, which is why it's called a variable.
* **Usage:** Variables are used when you need to store data that can change or when you don't initially know the value that will be stored.
* **Declaration:** The creation of a variable in a program usually requires at least specifying the variable's name and sometimes also its type.
* **Example:** In a program, you might have a variable named `age` that stores the age of a user. This age can be updated or changed as needed.

**Constants**

* **Definition:** A constant is similar to a variable in that it also represents a storage location with a name and value. However, once a constant is assigned a value, that value cannot be changed (it's constant).
* **Immutability:** The value of a constant remains the same throughout the program. Attempting to change it once it is set will result in a compile-time error.
* **Usage:** Constants are used to store values that are known before execution and do not change over the course of the program. They make programs easier to read and maintain, as their values are defined at one place and not scattered throughout the code with potential changes.
* **Declaration:** Declaring a constant usually involves specifying its name, type, and value. The syntax for declaring constants varies between programming languages.
* **Example:** In a program, you might have a constant named `PI` with a value of `3.14159`, representing the mathematical constant Pi.

#### Key Differences

* **Mutability:** Variables are mutable (their values can change), whereas constants are immutable (their values cannot change once set).
* **Purpose:** Variables are used for values that change during program execution, like counter values in loops, user inputs, etc. Constants are used for fixed values like configuration settings, error codes, or fixed mathematical values.

#### Conclusion

Understanding and correctly using constants and variables are fundamental in programming. They help in managing and manipulating data efficiently, ensuring that code is not only functional but also readable and maintainable.


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