Increment a variable in PowerShell in functions

You are running into a dynamic scoping issue. See about_scopes. Inside the function $incre is not defined so it is copied from the global scope. The global $incre is not modified. If you wish to modify it you can do the following.

$incre = 0

function comparethis() {
    #Do this comparison

    $global:incre++
    Write-Host $global:incre
}

comparethis #compare 2 variables
comparethis #compare 2 variables
comparethis #compare 2 variables
comparethis #compare 2 variables

Write-Host "This is the total $incre"