Numbers change inside variables for powershell - powershell

Question

I am literally just trying to convert a string with week and day information to numbers and store it as variable, yet something really funky is happening, as of now, I have tested this behavior in 4 PCs, and in Powershell 5 and 7 its happening all over the place.
$UP_Down = "6w0d"
[int]$weeks = if ($Up_Down -match "w"){$Up_Down[$($Up_Down.IndexOf('w')-1)]}Else{0}
[int]$days = if ($Up_Down -match "d"){$Up_Down[$Up_Down.IndexOf('d')-1]}Else{0}
[int]$totaldays = (7 * $weeks) + $days
Now the data from the initial variable is obviously 6 weeks and 0 days to which I have to convert to 42 Total days (this is just an example, its happening regardless of combination)
However the following is the Funky results I get which I have elaborated by Write-Output
Weeks If statement results by itself 6
Weeks variable results 54
days If statement results by itself 0
days variable results 48
totaldays variable results are 426
The problem occurs regardless of what numeric datatype I use
Ironically the Variables have the correct value if i DO NOT assign datatype to them, BUT ,
the moment it hits (7*$weeks) even IF the $weeks is correct the value outputted 426, and remember no [int]etc anywhere
What am I doing wrong?

Answer 1

The problem is, that you are not converting the number inside the string "6" to the number 6, but the character '6' to its value according to the underlying character encoding scheme that is 54 in the case of ASCII. Same with the day: '0' has a value of 48. 7 * 54 + 48 = 426.
See the difference:
PS C:\Users\name> [int]"6"[0]
54
PS C:\Users\name> [int]"6"
6
When extracting an element of the string through indexing with [0] you get a character instead of a string of length 1. A cast to int will then return the ASCII value of this character.

Answer 2

You're indexing ([...]) into string $Up_Down, which means you're returning a single character, i.e. a [char] (System.Char) instance.
Casting a [char] to [int] yields its Unicode code point ("ASCII value"), not the digit that the character happens to represent.
For instance, the character 6 is Unicode character DIGIT SIX with code point U+0036; 0036 is the hexadecimal form of the numeric code point, and the decimal form of hexadecimal 0x36 is 54.
PS> [int] "6w0d"[0]
54 # !! Same as: [int] [char] "6"
To interpret the character as a digit, you need an intermediate [string] cast:
PS> [int] [string] "6w0d"[0]
6 # OK - a string is parsed as expected; same as: [int] "6"
If you cast a string rather than char to [int], PowerShell effectively calls System.Int32.Parse behind the scenes as follows: [int]::Parse($string, [cultureinfo]::InvariantCulture).
Note that PowerShell has no char literals - unlike in C#, '...' quoting also produces strings (verbatim ones), and [int] '6' yields integer 6, just like [int] "6" does.
Conversely, you need an explicit [char] cast to convert a single-character string literal to a [char]; e.g., [char] '6'; a multi-character string would cause the cast to fail.
The solution in the context of your command:
[int]$weeks = if ($Up_Down -match "w"){[string] $Up_Down[$Up_Down.IndexOf('w')-1]} Else {0}
[int]$days = if ($Up_Down -match "d"){[string] $Up_Down[$Up_Down.IndexOf('d')-1]} Else {0}
However, I suggest solving the problem differently:
[int] $totalDays = 0
if ($UP_Down -match '^(?:(?<weeks>\d+)w)?(?:(?<days>\d+)d)?$') {
[int] $weeks, [int] $days = $Matches.weeks, $Matches.days
$totalDays = 7 * $weeks + $days
} # else: string wasn't in expected format.

Answer 3

others have shown you why the problem hit you, so this is just an alternate way to get the total day count. [grin]
what it does ...
fakes reading in a text file of Week/Day codes
when ready to use real data, remove the entire #region/#endregion block and use Get-Content.
iterates thru the list
splits on the w
trims away the trailing d
assigns the resulting strings to the two [int] variables on the left of the =
this forces the two number strings to become number objects.
calcs the total days
displays the week/day code, week count, day count, and total days
the code ...
#region >>> fake reading in a list of week/day codes
# in real life use Get-Content
$WD_List = #'
6w0d
3w3d
0w1d
66w6d
9w1d
'# -split [System.Environment]::NewLine
#endregion >>> fake reading in a list of week/day codes
foreach ($WL_Item in $WD_List)
{
[int]$WeekCount, [int]$DayCount = $WL_Item.Split('w').TrimEnd('d')
$TotalDays = ($WeekCount * 7) + $DayCount
$WL_Item
$WeekCount
$DayCount
$TotalDays
'=' * 20
}
the output ...
6w0d
6
0
42
====================
3w3d
3
3
24
====================
0w1d
0
1
1
====================
66w6d
66
6
468
====================
9w1d
9
1
64
====================