How can I Write-Output a PowerShell process object's ExitCode?

I need your help determining why I can’t output a PowerShell script process ExitCode and how to fix this. I think it has something to do with the data type of the result of the Start-Process command and the ExitCode property within it (which according to the error message at bottom here seems to be of "AnyType").

I have a simple CMD batch file named out.bat like this:

@echo off
echo Hello World, it's %1!

Then I have a seven-line PowerShell script named out.ps1, like this:

1.  $a = "C:\Temp\"
2.  $b = "out.txt"
3.  $c = "out.bat"
4.  $process = Start-Process -FilePath "${a}${c}" -ArgumentList "123" -RedirectStandardOutput ${a}${b} -Wait -PassThru
5.  Get-Content ${a}${b}
6.  Write-Output $process.ExitCode
7.  Write-Output "Error: $process.ExitCode"

My PowerShell script does successfully output the error code sent back by my CMD batch script file and output it per the sixth line above.

Hello World, it's 123!
0

However, the last line fails with,

Cannot convert value to type System.String.
At line:7 char:1
+ Write-Output "Error: $process.ExitCode"
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvalidCastFromAnyTypeToString

How can I get line 7 to simply output the following?

Error: 0

>Solution :

You have to use a sub-expression $(..) operator to have it evaluate the reference of that property:

Write-Output "Error: $($process.ExitCode)"