Perl does its arithmetic with double-precision floating point, so you probably get 52-bit precision.

for (49..54) {
  $x=2**$_;
  $y = $x + 1.1;
  print $_, "\t", $y-$x;
}

49    1.125
50    1
51    1
52    1
53    2
54    0
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In C++, the size of integer types isn't specified, but long long is probably 64 bits.

If you want to deal with really big numbers, you need to use a package like Math::BigInt.

If you only use ++ and reverse on your "numbers", perl's increment magic will make it Just Work (TM).

$x="100000000000000000000";
$x++;
print $x, "\n";
$x += 1;
print $x, "\n"';

100000000000000000001
1e+20
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