PowerShell 03 - Variables and Data Types

*Chapters:*
1. (00:42) Launching Integrated Scripting Environment (ISE), Administrative vs. Normal
2. (2:13) Comment Tags
3. (5:36) Declaring Variables and Assigning Values
4. (7:56) The Assignment Operator
5. (10:53) Strongly Typed vs. Loosley Typed
6. (11:54) Different Data Types, Type Casting and Conversion
7. (13:41) The Special Variable $null
8. (14:14) Variable Scope, Global vs. Local
9. (19:52) Assigning and Returning Values, Consequences of Wrong Data Types
10. (32:22) Output to the Console: Write-Host("") and Write("")
11. (37:08) Input from the Console: Read-Host()

[OneByteAtATime]

Source Code:
#1. Declaring a variable
$MyVariable;
<# #>
#Note: Variables are NOT case-sensitive in PowerShell. However, my background is in C++ and Java,
#which are case sensitive languages, I try to keep my POSH code case-sensitive too. Also, if you
#want to script in Linux? It's a case sensitive environment. So it's just good practice to
#discipline yourself to code in a tightly case sensitive manner.

#Note: PowerShell is not strongly data-typed like C++ or Java. In those languages, you need to
#declare the type and size of data when you create variables, and you can only store data of
#the correct type inside the correct type and size variable. This gives C++ and Java tight
#control over memory management and provides indirect access to objects stored in memory
#on the free store or the heap. This makes C++ and Java powerful and efficient, but complicates
#their usage. PowerShell on the other hand makes declaring variables easy. It is NOT strongly
#data-typed and you can create a generic variable in PowerShell and store just about any data
#type inside it. This decreases efficiency, but increases ease of use.

<# #>

#2. Declaring and Initializing a variable
$MyVariable = $null;
$MyStringVariable = "";
$MyNumberVariable = 0;

<# #>

#3. Assigning a value to a variable
$MyVariable = "Fluttershy";
$MyStringVariable = "Friendship is Magic";
$MyNumberVariable = 5 + 5;

<# #>

#4. Variable Scope - Global vs. Local

#Global (Single instance accessible to all functions in a program)
$global:MyVariable = $null;
$global:MyVariable = "Twilight Sparkle";

#Local (Multiple instance inside each function, accessible only to that function)
$MyVariable = $null;
$MyVariable = "Rainbow Dash";

<# #>

#Global Namespace = "The Infinite Multiverse"


function Universe_01
{
#Local NameSpace
= "Rarity"; #only accessible in Universe 1

= "Twilight1"; #accessible in any universe
}

function Universe_02
{
#Local NameSpace
= "Rarity"; #only accessible in Universe 2

= "Twilight2"; #accessible in any universe
}

<# #>

#5. The ASSIGNMENT Operator

#Note: A common misconception people frequently make in programming language is confusing the meaning "=".
#In math, the "=" means "equals. So if I write the expression "a = 7", I am saying "a equals 7". However,
#this is NOT that case in programming. The "=" does not mean "equals" in programming, but rather "assign".
#So if I write the expression "a = 7" in code? What I am saying is "assign the value of 7 to variable a",
#or "store the value of 7 inside container a". The assignment operator always says "take what is on the
#left and store it in the object on the right". Changing the way you think about "=" will help you avoid
#many logic and syntax errors in the future.

$a = 444; #assigns value of 444 to variable a, takes 444 on left and stores it in a on the right

<# #>

#6. Explicitly typing/casting a PowerShell Variable

#Note: Powershell tries to simplify variable declaration and usage by not forcing strong data typing.
#To achieve this? It treats most data as string data by default. String data is a collection of chars.
#Unfortunately, this can create unexpected outcomes and create errors in calculations. For example:

#A. This calculates correctly, PowerShell auto-chooses the correct data types
$ANumber = 222;
$MyNumber = $ANumber * 2;
Write("MyNumber is now: " + $MyNumber);

#Above, eeverything calculates correctly and MyNumber displays as 444.

#B. This calculates incorrectly, PowerShell choses wrong data type since input is a string
$MyNumber = Read-Host("Please enter a number");
$MyNumber = $MyNumber * $MyNumber;
Write("MyNumber squared is: " + $MyNumber);

#If I enter "4"? I should get the square of 4. But because Powershell treats it as a string data type instead
#of an integer data type? It displays the incorrect value of "4444" instead of "16". Powershell is treating
#the data type as a String, so it displays the char "4" 4 times. It's not treating it as integer data.

#C. We can help powershell as programmers by explicitly declaring the data type of the input variable. The syntax
#for this is very similar to type-casting in C++ and Java, where you convert one data type to another. In
#Powershell, to explicitly declare the data type of a variable use [] and insert the explicit data type in between.

[Int]$MyNumber = Read-Host("Please enter a number");
$MyNumber = $MyNumber * $MyNumber;
Write("MyNumber squared is: " + $MyNumber);

#Notice when I enter the exact same value "4" above? It now calcualtes the square correctly as "16".

#Another example:
[DateTime]$FooledMe = "April 1, 2020";
$CurrentDate = Get-Date;
$Days = ($CurrentDate - $FooledMe).Days;
Write-Host "Worst prank ever $Days day(s) ago.";

#Example above explicitly forces the string data "April 1, 2020" into a [DataTime] class oject in PowerShell.
#Now that it is the right data type? It can be used for calculations.

<#
Here are some values you can EXPLICITLY convert/cast to in PowerShell:

[Int] = 32-bit integers
[Int32] = 32-bit integers
[Float] = floating point, for large numbers or extra decimal precision
[Single] = floating point, for large numbers or extra decimal precision
[Bool] = boolean values, either $true or $false
[String] = a string of text
[Array] = an array, a collection of variable objects
[DateTime] = date and time object
[TimeSpan]= a time interval
[Guid] = GUID 32-byte identifier
[HashTable] = hash table with key-value pairs
[ScriptBlock] = powerShell script block
[PsObject] = a powerShell object
[XmlDocument] = an XML document
[Regex] = a regular expression
#>

#Note: You can use the methods "GetType()" to get a variable's data type if you aren't sure.
$b = 444;
$b.GetType().Name

<# #>
#More Examples:

#----Example 1: Reading string data and storing it in

function Pony_Database
{
$UserName = Read-Host("Please enter your NAME");
$UserAge = Read-Host("Please enter your AGE");
$UserSpecies = Read-Host("Please enter your SPECIES");
$UserGender = Read-Host("Please enter your GENDER");

Write("`nStats:`n");
Write("Name: " + $UserName);
Write("Age: " + $UserAge);
Write("Species: " + $UserSpecies);
Write("Gender: " + $UserGender);
}



#----Example 2: Reading string data and storing it in

function Guess_My_Number
{
$MyNumber = 444;

$BestGuess = Read-Host("What is MyNumber?");

if($BestGuess -EQ $MyNumber)
{ Write("What luck! You guessed my number!"); }
else
{ Write("Sorry. That was NOT my number."); }

}


#Title: PowerShell - Module 01 - Data Types and Variables
#Author: Carly S. Germany
#Date: 04/23/2020

[mohdridzuanramli]

did you compose the music by yourself?niceeee...

[BalvinderSingh-uhmy]

I find it difficult to read what you are writing on the fly on the screen. So I can't do your videos the justice they deserve :-( Took me some time to find write-host ("`n`n") 39 mins. Because I am a bit thick but well worth it because you have a unique teaching style which I find very helpful.