Beginning Web Development With Perl : From Novice to ... - Nabo

296APPENDIX ■ PERL BASICSThe last arithmetic operator remainder, or modulo operator. This calculates the remainderwhen one number divides another. For example, 6 divides into 15 twice, with a remainderof 3, as our next program will confirm:#!/usr/bin/perl -w# arithop8.plprint "15 divided by 6 is exactly ", 15 / 6, "\ n";print "That's a remainder of ", 15 % 6, "\ n";$ perl arithop8.pl15 divided by 6 is exactly 2.5That's a remainder of 3$The modulo operator has the same precedence as multiply and divide.Bitwise OperatorsUp to this point, the operators worked on numbers in the way we think of them. However, aswe already know, computers don’t see numbers the same as we do; they see them as a string ofbits. These next few operators perform operations on numbers one bit at a time—that’s whywe call them bitwise operators. These aren’t used quite so much in Perl as in other languages,but we’ll see them when dealing with things like low-level file access.First, let’s have a look at the kind of numbers we’re going to use in this section, just so weget used to them:• 0 in binary is 0, but let’s write it as 8 bits: 00000000.• 51 in binary is 00110011.• 85 in binary is 01010101.• 170 in binary is 10101010.• 204 in binary is 11001100.• 255 in binary is 11111111.Does it surprise you that 10101010 (170) is twice as much as 01010101 (85)? It shouldn’t—when we multiply a number by 10 in base 10, all we do is slap a 0 on the end, so 21 becomes210. Similarly, to multiply a number by 2 in base 2, we do exactly the same.People think of bitwise operators as working from right to left; the rightmost bit is calledthe least significant bit and the leftmost is called the most significant bit.The AND OperatorThe easiest bitwise operator to fathom is called the AND operator, and is written &. This comparespairs of bits as follows:• 1 and 1 gives 1.• 1 and 0 gives 0.