Variables and Constants

Understanding Variables and Constants

Variables

Variables are named locations in computer memory used to store data.
This data or value can be changed, or varied, during program execution, hence the term ‘variable’.
Every variable has a datatype, which identifies the type of data it should store. Examples of datatypes include integers, boolean, float, string etc.
Variable names should be descriptive and follow a naming convention like CamelCase or underscores to increase program readability.
A variable must be declared before it can be used in a program.

Constants

Constants are similar to variables as they are also named locations to store data.
However, the value of a constant cannot be changed during program execution, making it constant.
Constants are also required to be declared before they can be used in a program.
Constants are usually used to define fixed values that should not be altered, such as PI, gravity, tax rates etc.
Like variables, constants also have datatypes.

Declaration and Assignment

Declaration is the process of defining a variable or constant in a program.
In many programming languages, you declare a variable by stating its datatype followed by its name.
Assignment refers to the action of initializing or updating the value of a variable.
You can declare and assign a variable or constant at the same time or in separate steps.
In most languages, you use the assignment operator ‘=’ to assign a value to a variable.

Scope of Variables and Constants

Scope describes the region of code where a variable or constant can be accessed.
Variables declared within a function or a loop, known as local variables, are only accessible within that function or loop.
Variables declared outside all functions, known as global variables, are accessible throughout the entire program.
Constants are generally global and can be accessed throughout the entire program.

Lifetime of Variables and Constants

The lifetime of a variable or constant begins when it is declared and ends when the program stops running or the function it was declared in is finished executing.
Local variables have shorter lifetimes as they cease to exist when the function they are declared in ends.
Global variables and constants usually have lifetimes that span the entire execution time of the program.

Key Takeaway

Understanding and using variables and constants correctly is fundamental to successful programming and avoids common errors.