$operator = <STDIN>;
chomp $operator;
if ($operator eq '+')
{
   $result = $a + $b;
}
elsif ($operator eq '-')
{
   $result = $a - $b;
}
elsif ($operator eq '*')
{
   $result = $a * $b;
}
else
{
   die "unknown operator \"$operator\"\n";
}

##</code><code>##

$first=<STDIN>;
$second=<STDIN>;
$operator=<STDIN>;
chomp $first;
chomp $second;
chomp $operator;

$expression = "$first $operator $second";
print "$expression:\n";

$result = eval $expression;
if ($@)  # ($@ is set by eval if something went wrong)
{
    print "oh no!: $@\n";
}
else
{
    print "$result\n";
}