CSC - Variables and Constants

Programming is all about writing the most efficient code to achieve a specific task
By using variables and constants, we're able to store values temporarily
These values can then be referenced or re-used to perform other tasks and functions
Variables and constants are used in both programming and pseudocode

A variable is a memory location that has its own associated name (known as an identifier)
Variables are simply temporary stores that a program can access to reference or re-use a value during execution
Unlike constants, variables can vary and have changing values
Variables are used religiously throughout programming as they streamline efficienecy and allow for easier referencing

A constant is another memory location that, like a variable, consists of an identifier and a value
Unlike a variable, however, a constant does not change in value
These are handy for fixed values such as the mathematical symbol Pi
Pi is a constant is the value does not change
Pi is given a symbol to represent the fixed value number, which is known as its identifier

A naming convention is simply a set of rules put in place to ensure organization and consistency of variables and constants
Many programming languages allow for a vast array of naming options for variables and constants
How variables and constants are named in a program are often up to the discression of the developer(s)
They're used to reduce the effort needed to read code as well as maintain consistency
Some variables and constants have system or programming language restraints, such as words reserved for predefined functions
It's generally sought after to name variables and constants with clear English words that relate to their use

A local variable is a variable that is only accessible in the current code or module
To write code you need to set up numbers and words that can be read by the program
These numbers and words are given data types and values so they can be read.
For calculating the area of a rectangle we need to be able to use the following variables
- length
- width
- total area
To make length, width and total area, variables we need a data type and a value (VB example)
- Dim length As Double
- Dim width As Double
- Dim totalArea As Double

The purpose of a global variable is to provide a variable that is accessible from anywhere within the program. eg so other functions or modules can use them.
They are placed prior to other modules or functions.
So, a global variable can be used in a module, only if it is in the code prior to that code.
Ideally you want a variable to change, but as a global variable is used by different modules, it will cause confusion when it is changed.
Global variables are not used much as they are limited in what they can do.

A parameter is a referenced variable or constant that is passed to a function or module
We define a parameter of a function or module and tell the program what values are needed for it to operate
These parameters can be passed into and out of a function or module
They usually have brackets (parentheses) around them so are easy to find.

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ProgrammingSequence, selection, iteration, procedures, functions, modules, parameters, compilers, interpreters