I have the following code:
SN.get_Chars(5)
SN is a string so this should give the 5th Char Ok!
Now i have another code but : SN.get_Chars(0x10)
I wonder what 0x10 is? Is it a number? If it's so, then what is it in decimal notation?
+35
A:
0xNNNN represents, in C at least, a hexadecimal (base-16 because 'hex' is 6 and 'dec' is 10 in Latin-derived languages) number, where N is one of the digits 0 through 9 or A through F (representing 10 through 15), and there may be 1 or more of those digits in the number. The other way of representing it is NNNN16.
It's very useful in the computer world as a single hex digit represents four bits (binary digits). That's because four bits, each with two possible values, gives you a total of 2 x 2 x 2 x 2 or 16 (24) values. In other words:
_____________________________________bits____________________________________
/ \
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
| bF | bE | bD | bC | bB | bA | b9 | b8 | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 |
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
\_________________/ \_________________/ \_________________/ \_________________/
Hex digit Hex digit Hex digit Hex digit
A base-X number is a number where each position represents a multiple of a power of X.
In base 10, which we humans are used to, the digits used are 0 through 9, and the number 730410 is:
- (7 x 103) = 700010 ; plus
- (3 x 102) = 30010 ; plus
- (0 x 101) = 010 ; plus
- (4 x 100) = 410 ; equals 7304.
In octal, where the digits are 0 through 7. the number 7548 is:
- (7 x 82) = 44810 ; plus
- (5 x 81) = 4010 ; plus
- (4 x 80) = 410 ; equals 49210.
In binary, where the digits are 0 and 1. the number 10112 is:
- (1 x 23) = 810 ; plus
- (0 x 22) = 010 ; plus
- (1 x 21) = 210 ; plus
- (1 x 20) = 110 ; equals 1110.
In hexadecimal, where the digits are 0 through 9 and A through F (both groups giving 0 through 15). the number 7F2416 is:
- (7 x 163) = 2867210 ; plus
- (F x 162) = 384010 ; plus
- (2 x 161) = 3210 ; plus
- (4 x 160) = 410 ; equals 3254810.
Your relatively simple number 0x10, which is the way C represents 1016, is simply:
- (1 x 161) = 1610 ; plus
- (0 x 160) = 010 ; equals 1610.
As an aside, the different bases of numbers are used for many things.
- base 10 is used, as previously mentioned, by we humans with 10 digits on our hands.
- base 2 is used by computers due to the relative ease of representing the two binary states with electrical circuits.
- base 8 is used almost exclusively in UNIX file permissions so that each octal digit represents a 3-tuple of binary permissions (read/write/execute). It's also used in C-based languages and UNIX utilities to inject binary characters into an otherwise printable-character-only data stream.
- base 16 is a convenient way to represent four bits to a digit, especially as most architectures nowadays have a word size which is a multiple of four bits.
- base 64 is used in encoding mail so that binary files may be sent using only printable characters. Each digit represents six binary digits so you can pack three eight-bit characters into four six-bit digits (25% increased file size but guaranteed to get through the mail gateways untouched).
- as a semi-useful snippet, base 60 comes from some very old civilisation (Babylon, Sumeria, Mesopotamia or something like that) and is the source of 60 seconds/minutes in the minute/hour, 360 degrees in a circle, 60 minutes (of arc) in a degree and so on [not really related to the computer industry, but interesting nonetheless].
- as an even less-useful snippet, the ultimate question and answer in The Hitchhikers Guide To The Galaxy was "What do you get when you multiply 6 by 9?" and "42". Whilst same say this is because the Earth computer was faulty, others see it as proof that the creator has 13 fingers :-)
paxdiablo
2009-03-28 05:54:06
+1 for thoroughness and a math lesson, but don't forget poor old base-2 ;-)
Robert Paulson
2009-03-28 06:00:29
base 60 would be babylon.
Ikke
2009-03-28 06:24:26
I don't like to speak authoritatively on things I know little about. It may have been the Babylonians, Sumerians or Mesopotamians - you may just as well say the Iraqis for all I'd know. I'll leave that to the history buffs (my interest in ancient history is adequate but not comprehensive).
paxdiablo
2009-03-28 06:58:34
Iraq doesn't exactly fall under "ancient history", as it was founded in the 20th century :-)
EddieD
2009-03-28 12:18:59
@EddieD, I meant it's all in the same area. I think. My geography is far worse than my history :-)
paxdiablo
2009-03-28 13:14:55
+1 for incredibly informative =)
David Thomas
2009-04-18 14:06:03
+! Fantastic answer!
LeopardSkinPillBoxHat
2009-04-21 06:59:50
I think it was in Voodoo Child that a 6 turned out to be 9.
Romain Hippeau
2010-05-06 03:19:27
why did they choose base 60?
Louis Rhys
2010-08-12 04:56:13
@Louis: old I am, young padawan, but 5000 years old not am I :-) Check out http://en.wikipedia.org/wiki/Sexagesimal - they seem to think it was because 60 has bucketloads of factors.
paxdiablo
2010-08-12 04:58:32
+1
A:
Notice that '10' is the representation of the base in the its base:
10 is 2(decimal) in base-2
10 is 3(decimal) in base-3
...
10 is 10(decimal) in base-10
...
10 is 16(decimal) in base-16 (hexadecimal)
...
10 is 1024(decimal) in base-1024
...and so on
jab
2009-04-21 06:51:49