It is possible to pass by reference in perl.
The argument list u get inside ur subroutine via @_
are implicit reference to values that were passed in from inside
from outside.i.e. if u pass in a list of strings,
inside the body of the sub,change those strings,then
they will be modified outside the subroutine.
sub ted {
my($add,$sub,$mul) = @_;
...
..
}