use Devel::Size qw(size);
use Devel::Peek;

sub info {
    print Dump($_[0]);
    print "size = ",size($_[0]),"  ($_[1])\n\n";
}

$num = 123;  # or int("123")
info($num, "integer");

$num .= "";
info($num, "integer stringified");


$str  = "123";
info($str, "string");

$str += 0;
info($str, "string numified");

$str += 45678900;
info($str, "... with bigger integer");

$str .= "";
info($str, "... re-stringified");

##</code><code>##

SV = IV(0x816983c) at 0x8192124
  REFCNT = 1
  FLAGS = (IOK,pIOK)
  IV = 123
size = 16  (integer)

SV = PVIV(0x8150b10) at 0x8192124
  REFCNT = 1
  FLAGS = (POK,pPOK)
  IV = 123
  PV = 0x81c9f18 "123"\0
  CUR = 3
  LEN = 4
size = 32  (integer stringified)

SV = PV(0x814fb90) at 0x81ca934
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x81950f0 "123"\0
  CUR = 3
  LEN = 4
size = 28  (string)

SV = PVIV(0x8150b20) at 0x81ca934
  REFCNT = 1
  FLAGS = (IOK,pIOK)
  IV = 123
  PV = 0x81950f0 "123"\0
  CUR = 3
  LEN = 4
size = 32  (string numified)

SV = PVIV(0x8150b20) at 0x81ca934
  REFCNT = 1
  FLAGS = (IOK,pIOK)
  IV = 45679023
  PV = 0x81950f0 "123"\0
  CUR = 3
  LEN = 4
size = 32  (... with bigger integer)

SV = PVIV(0x8150b20) at 0x81ca934
  REFCNT = 1
  FLAGS = (POK,pPOK)
  IV = 45679023
  PV = 0x81950f0 "45679023"\0
  CUR = 8
  LEN = 12
size = 40  (... re-stringified)