How to modify Powershell script to use 0 as current day

I would like to modify this Powershell script so if you enter the number 0, it will accept today's date.
If Enter is pressed, it should not move ahead until only a Number is entered for the amount of days back.

Thanks in advance.

[code]$userDays = Read-Host -Prompt "How many days ago is this report for (no input = today)"
If ($userDays -ne $null) {
      Try {
            $daysAgo = [Int32]$userDays
      } Catch {
            Write-Warning "'$($userDays)' is not a number; will use 1 day!"
            $daysAgo = 1
      }
} Else {
      $daysAgo = 1
}
###SETUP START###
#-------DO NOT MODIFY-------#
      #Yesterdays Date
            $date = ((Get-Date).AddDays((-1 * $daysAgo))).ToString("MMM/dd/yyyy")
###SETUP END###/code]