Going In-Depth On Powershell Arrays

Kevin Marquette has a tour de force on Powershell arrays:

When your array is a collection of string or integers (value types), sometimes you will want to update the values in the array as you enumerate them. Most of the iteration loops above use a variable in the loop that holds the value. If you update that variable, the original value in the array is not updated.

The exception to that statement is the for loop. If you are wanting to walk an array and update values inside it, then the for loop is what you are looking for.

    for ( $index = 0; $index -lt $data.count; $index++ )
    {
        $data[$index] = "Item: [{0}]" -f $data[$index]
    }

This examples takes a value by index, makes a few changes, and then uses that same index to assign it back.

This is a book chapter-length blog post full of good information.