$totalamount = 0;
$companyname = "";

##</code><code>##

$totalamount = undef;
$companyname = undef;

##</code><code>##

$totalamount = $companyname = undef;

##</code><code>##

if ((length($companyname)>0) && ($anotherstring eq 'DOIT')) { ... }

##</code><code>##

if (($companyname) && ($anotherstring eq 'DOIT')) { ... }