 Array Pointers Can Be Backwards, (Kind of) |
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 May 3 2008, 01:08 AM
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#1
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Premium Member  Group: Members Posts: 150 Joined: 9-April 07 From: Nebraska Member No.: 41,301  |
I just found this out today:
When you're using arrays, when you reference a certain index, you can switch the pointer and the subscript around. I know I'm not explaining that very good, but here's and example: CODE int a[] = {1,2,3,4,5,6,7,8,9,10,11}; int b =1; int c[] = {0,-5,11,0,0,5,0,0,0}; cout << b[a][c]; //Same as c[a[b]]; See? 'b' is actually just an integer, it's not an array, or pointer, or anything. Usually, you would have to put the array first, then an integer. Like if you have an array of type int, of length 5, you could reference something at index 3 using: CODE a[3] //OR 3[a] It doesn't really make sense, but I found this on a forum, as someone's signature: CODE int main() { char o[1920]={0}; int _; double l[]={0,-5,11,0,0,5,0,0,0},_1=0.174533; for(_=0;_<36;++_) (((int)(2[l]=((cos(_1)*(4[l]=2[l]))+(sin(_1)*7[l])))+12)*80 +((int)(7[l]=((cos(_1)*7[l])-(sin(_1)*4[l])))+40))[o]=_<27?(((int)(8[l]=((cos(-_1) *(6[l]=8[l]))+(sin(-_1)*5[l])))+8)*80+((int)(5[l]=((cos(-_1)*5[l])-(sin(-_1)*6[l]))) +40))[o]=(((int)(1[l]=((cos(_1)*(0[l]=1[l]))+(sin(_1)*3[l])))+16)*80+((int)(3[l]= ((cos(_1)*3[l])-(sin(_1)*0[l])))+40))[o]='*':'*'; _=0; while(_<1920)putchar(_++[o]); } //don't forget to include iostream and use namespace std That was actually more garbled when it was in their signature, I just indented it, and added new lines where the semicolons were. What really confused me was that they used and underscore as a variable(hard to see in a signature, I thought it was a space or something), and there were some parts where they switched the pointer and the subscript for an array (like in that last 'while'). All this really does is print out a bunch of asterisks in the shape of an 's' with a circle around it. I'm pretty sure that the way they coded that isn't good practice, they were just trying to condense it a lot so they could fit it in their signature. But hey, I guess I learn something new every day. 
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May 11 2008, 05:51 PM
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#2
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Super Member Group: Members Posts: 399 Joined: 14-November 04 From: Elysium Member No.: 2,280 |
 WoW! That's really cool actually. Heh, after forever I'm learning something new about C++. yay. Wouldn't that mess up if both were defined though? E.g. your a[3] = 3[a] thing. If I made an int array named 3 and an int array named a, that wouldn't work anymore, would it?
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May 20 2008, 07:13 PM
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#3
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Premium Member Group: Members Posts: 150 Joined: 9-April 07 From: Nebraska Member No.: 41,301 |
Actually I haven't really tried that. I didn't even think of it.
I'm pretty sure it's impossible to name an array '3', though, but I get what you mean. |
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May 23 2008, 02:30 PM
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#4
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Super Member Group: Members Posts: 399 Joined: 14-November 04 From: Elysium Member No.: 2,280 |
QUOTE I'm pretty sure it's impossible to name an array '3', though, but I get what you mean. Hmm. This has always been true. That being said, I think I've found my favorite line of non-ANSI code ever: 3[3]=3; |
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Jun 1 2008, 07:02 PM
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#5
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Member [Level 1] Group: [HOSTED] Posts: 61 Joined: 1-June 08 Member No.: 62,997 |
Haha, that is imposible, You cannot do that. You should obtain a segmentation fault for doing so. If you have an array j={0,1,2,4,5,6}, if you refer to j you will obtain the adress of the first object in the array.
And 4[j] will lead in a segmentation fault or will read a piece of code from the program. |
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Aug 18 2008, 02:27 AM
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#6
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Trap Double Mocha Member Group: Members Posts: 2,360 Joined: 21-September 07 Member No.: 50,369 |
pointers
Array Pointers Can Be Backwards How do you input a word/string from the keyboard then print it and it's reverse using pointers? help me please! -question by ishi |
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Aug 27 2008, 01:02 PM
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#7
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Member [Level 1] Group: [HOSTED] Posts: 58 Joined: 30-July 08 From: Bronx, NY Member No.: 65,739 |
QUOTE(hippiman @ May 2 2008, 09:08 PM)  I'm pretty sure that the way they coded that isn't good practice... It's probably not but there are competitions where programmers vie to create highly "obfuscated" code of the kind you've listed. That kind of code usually takes advantage of little known quirks in the syntax of a language and/or compiler like the one you've listed here. Google 'obfuscated code' and you will no doubt find even more oddities in code syntax and their applications. One thing though, some compilers maintain strict adherence to the specifications of its particular language, therefore some obfuscations can only be run with certain compilers. That's probably why @seba1killer got the errors he/she listed. This post has been edited by dimumurray: Aug 27 2008, 01:03 PM |
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Aug 28 2008, 08:10 AM
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#8
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Newbie [Level 1] Group: [HOSTED] Posts: 14 Joined: 28-August 08 Member No.: 66,981 |
QUOTE(iGuest-ishi @ Aug 18 2008, 12:27 PM) pointers Array Pointers Can Be Backwards How do you input a word/string from the keyboard then print it and it's reverse using pointers? help me please! -question by ishi Hopefully this is what you meant: CODE #include <cstdio>
using namespace std; int main() { char str[200]; for (int i = 0; i < 200; i++) i[str] = 0; gets(str); int i = 0; while (i[str] != 0) { putc(i[str], stdout); i++; } getchar(); return 0; } |
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