Powershell input piping issue

Question

I am not able to run this simple powershell program

[int]$st1 = $input[0]
[int]$st2 = $input[1]
[int]$st3 = $input[2]
[int]$pm = $input[3]
[int]$cm = $input[4]

$MedMarks = $st1 + $st2 + $st3 - ($pm + $cm)
Write-Host "Med Marks  $MedMarks"

I am trying to run it with input pipeline like this

120, 130, 90, 45, 30 | .\sample_program.ps1

I am consistently getting this error

Cannot convert the "System.Collections.ArrayList+ArrayListEnumeratorSimple" value of type
"System.Collections.ArrayList+ArrayListEnumeratorSimple" to type "System.Int32".

Answer 1

If you inspect $input like this:

PS> function f { $input.GetType().FullName } f
System.Collections.ArrayList+ArrayListEnumeratorSimple

then you can notice, that $input is not a collection, but an enumerator for one. So, you do not have random access with indexer for bare $input. If you really want to index $input, then you need to copy its content into array or some other collection:

$InputArray = @( $input )

then you can index $InputArray as normal:

[int]$st1 = $InputArray[0]
[int]$st2 = $InputArray[1]
[int]$st3 = $InputArray[2]
[int]$pm = $InputArray[3]
[int]$cm = $InputArray[4]