Variable, Constants and DataType

Variable

Variable is a container that acts like a basket. Basically, it holds information in memory (RAM) such as a number.

The data can be taken in and out of the vairable in the same way you place an apple in and out of a basket.

The variable is used to store data in a program until it is needed.

Anything enetered via keyboard (input) has to be stored into a variable. Before a variable can be used to store data, it must be declared (created).

This means that a location in the RAM must be created with the correct amount of space, but as RAM has a complicated memory addres using numbers a simple identifier is used.

So each variables uses an English word that is meaningful to the data.

The variables identify is a reference to the real address space in memory.

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Constants

Constants are a way of storing a value that will not be changed. Constants aren't variables and therefore may not be modified.

Constants can be used stoore all the different datatypes this included numbers, boolean and strings.

tip

Don't create a constant to represent information that you expect to change at any time.

Example:

Const Double pie = 3.142;

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Differences between C# and Python

C#

C# requires you to declare the variable and then use it.

public class Program
{
    public static void Main(){

    String name = "";
    name = "John";

    // You can declare and assign a value at the same time
    name = "John";
    }
}

Python

Python has no command for declaring a variable. A variable is created the moment you first assign a value to it.

name = "John"

note

String is used for C# but not for python. String is called a data type. In Python it selects the one it thinks you need.

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Datatype

The data type says how much memory will be allocated to that variable.

info

Some languages such as python do not need you to include a data tye when declaring a variable.

Datatype will tell the computer what type of data the variable can store and how to handle the data.

note

Datatypes are important because it will ensure that enough space has been given to the value the variable will hold otherwise the program would crash with a memory overflow problem

Datatype	Size (in bits)	Values
byte	8	0 to 255
int (int32)	32	-2,147,483,648 to 2,147,483,647
int 16	16	-32,768 to 32,767
int 64	64	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
double	64	-1.79769313486232e308 to 1.79769313486232e308
string	varies	String of characters (a word)
bool	Boolean value	True or false
float	32-bit single-precision floating point type	-3.4 x 1038 to + 3.4 x 1038