Sample.PS1

cls
$psver=$PSVersionTable.PSVersion.Major

$mystr="aaa"
$myarr="aaa","bbb","ccc"
if($psver -eq "2")
{
    write-host "Executing on Version 2"
    $myarr -contains $mystr
}
elseif($psver -eq "5")
{
    write-host "Executing on Version 5"
    #$mystr -in $myarr  #this statement results in error on PS2.0 environment. Error message is "You must provide a value expression on the right-hand side of the '-' operator"
}