Friday, May 3, 2013

Powershell DIY: Absolute Value


Absolute value.  This is the best possible simple example of an “if” “ElseIf” statement.  An absolute value is the distance a number is from 0.  For 22 it is just that, 22.  For -22, the absolute value is 22.  In order to do this we are going to use the read-host command to gather the requisite value:

$a = Read-Host “Number?”

With this statement we are defining $a by asking the user with “Read-Host”.  The “Number?” is purely optional, but I always suggest using it to define the input.  Next we need to use the “If” statement.

If

If must always be followed by a statement in parentheses:

If ()

For our conditional statement we are going to use the -le condition.  We start with using the literal value of $a, ‘$a’ and the condition Less Than (-le) and define what exactly it is supposed to be less than, 0:

If ('$a' -le 0)

So What if $a is less than 0? We subtract it from 0 of course! Any negative number subtracted from 0 gives us the positive corresponding value.  Encapsulated in Braces ({}) we spell out the math equation:

{$a = 0 - ($a)}

In order to address a negative value we must further encapsulate it in parentheses, as we have done here.  Our completed “If” statement is:

If ('$a' -le 0) {$a = 0 - ($a) }

Now we must address positive values to balance the script.  We use the “ElseIf” statement for this:

ElseIf

And much like the “If” statement the condition is encapsulated in Parentheses () and the action is encapsulated in braces ({}):

ElseIf(){}

The conditional statement here is similar to the previous if statement, with one exception, the Less Than ( -le) has been replaced with a Greater Than (-ge) condition:

ElseIf ($a -ge 0){}

Since this statement is for a positive number, we don’t want it to actually do anything, so we balance both sides of the equation by making an obvious statement $a = $a

ElseIf ($a -ge 0){$a = $a}

With this we have stated this: “If $a is greater than 0, make $a equal $a.” In other words, Do nothing.  Last but not least, we tell the user the absolute value by using the variable alone:

$a

Here is the Finished product:

$a = Read-Host "Number?"
If ('$a' -le 0) {$a = 0 - ($a) }
ElseIf ($a -ge 0) {$a = $a}
$a

I am sure there is a command that does all this out there, but the purpose of this was to demonstrate math, addressing negative numbers, and If “ElseIf” statements.  As usual if you have a better way to do this, let me know!  The fastest way to learning is through collaboration!



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