The Big Programming Thread - Page 153

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Thread Rules
1. This is not a "do my homework for me" thread. If you have specific questions, ask, but don't post an assignment or homework problem and expect an exact solution.
2. No recruiting for your cockamamie projects (you won't replace facebook with 3 dudes you found on the internet and $20)
3. If you can't articulate why a language is bad, don't start slinging shit about it. Just remember that nothing is worse than making CSS IE6 compatible.
4. Use [code] tags to format code blocks.

SiPa

Germany129 Posts

August 01 2012 11:35 GMT

#3041

Doublepost, nvm.. pls delete

OPman

United States131 Posts

August 01 2012 14:12 GMT

#3042

I've been going through the Hands-on Python Tutorial (which is fantastic by the way) and i'm having trouble with one of the exercises. The gist of the exercise is to ask the user for input asking for a file to open, copy the contents, and write them to a new file with the characters in all uppercase. The new filename would be the same as the old one, but with "UPPER" preceding it. The last bit is the only part I can't figure out.

Here's what I have so far.


filename = input('What file would you like to make an UPPER file for? ')
sheit = open(filename, 'r')
contents = sheit.read()

newfile = open('UPPER'filename, 'w')  \\WTFSyntax
newfile.write(contents.upper())
filename.close()
newfile.close()

The 'UPPER' filename syntax is wrong, but I don't know the proper way to write it. Damn the site for not providing solutions >.<

xlep

Germany274 Posts

August 01 2012 14:19 GMT

#3043

never leaned python but google says: filename.upper() should work for ASCII strings

OPman

United States131 Posts

August 01 2012 14:30 GMT

#3044

On August 01 2012 23:19 xlep wrote:
never leaned python but google says: filename.upper() should work for ASCII strings

That works for making the filename FILENAME, I need to add the word "UPPER" before the filename and I think I figured that part out although the contents aren't being copied properly.

I changed this line here, and successfully made the new file, but the uppercase contents aren't copied over to it.


 newfile = open("UPPER"+filename, 'w')

The error I'm getting in the Shell is saying: 'str' object has no attibute 'close' referring to filename.

OPman

United States131 Posts

August 01 2012 14:35 GMT

#3045

Fixed -_-

Rather than filename.close(), I should have written sheit.close(). Since the file wasn't ever closed properly, it seems like the contents weren't actually saved to the new file.

[image loading]

EruIluvatar

Germany2 Posts

August 02 2012 03:09 GMT

#3046

Hello guys,
I'm attempting to learn C.
I've got the first version of K&R's "The C Programming Language" from 1978, when C wasn't even standardized by ANSI. I like the style of that book with the explanations and tasks after every block.

My problem: Sometimes I get confused, when i try to correct the outdated code examples in order to write valid code that is accepted by the current compilers without warnings and error messages.

Should I buy the second edition following the ANSI C standard from 1988 which is over twenty years old as well, despite it does not cover the newer standards or would it be better to buy an other book, that isn't published such a long time ago?
If you recommend the last alternative, please give me a suggestion for a book that you prefer (english or german)
Eru

ps. first post on TL - was only reading before

DumJumJmyWum

United States75 Posts

August 02 2012 03:13 GMT

#3047

On August 02 2012 12:09 EruIluvatar wrote:
Hello guys,
I'm attempting to learn C.
I've got the first version of K&R's "The C Programming Language" from 1978, when C wasn't even standardized by ANSI. I like the style of that book with the explanations and tasks after every block.

My problem: Sometimes I get confused, when i try to correct the outdated code examples in order to write valid code that is accepted by the current compilers without warnings and error messages.

Should I buy the second edition following the ANSI C standard from 1988 which is over twenty years old as well, despite it does not cover the newer standards or would it be better to buy an other book, that isn't published such a long time ago?
If you recommend the last alternative, please give me a suggestion for a book that you prefer (english or german)
Eru

ps. first post on TL - was only reading before

I would probably get the second version as it's still used today as a reference. It's what I used for my OS class a couple years ago that served me well, so I think it should work just fine without too many problems.

thOr6136

Slovenia1775 Posts

August 03 2012 10:58 GMT

#3048

Ok guys i have a question regarding c++

There is a function called FindFirstFile() and let's say we search for all COM files in some directory. Now when function finds first COM file, it saves its information in WIN32_FIND_DATA structure , and here is a problem, how can i get name of the file that was found?

EDIT: by getting it i mean like using it further down the program, not a specific name of file, more like a variable of some sort, if you know what i mean

Deleted User 101379

4849 Posts

August 03 2012 11:04 GMT

#3049

On August 03 2012 19:58 thOr6136 wrote:
Ok guys i have a question regarding c++

There is a function called FindFirstFile() and let's say we search for all COM files in some directory. Now when function finds first COM file, it saves its information in WIN32_FIND_DATA structure , and here is a problem, how can i get name of the file that was found?

From the documentation you linked it looks like a simple:


WIN32_FIND_DATA foo;
FindFirstFile(..., &foo);
printf("%s", foo.cFileName);

thOr6136

Slovenia1775 Posts

August 03 2012 11:07 GMT

#3050

ty sir

, this documentation confuses me sometimes

SgtCoDFish

United Kingdom1520 Posts

August 03 2012 11:13 GMT

#3051

The second edition should serve you very well if you want to learn from a book, since it follows the "C89" standard which is pretty commonly used even today. The newer standard "C99" still isn't too widely used for various reasons as far as I know although I don't do much work in C. That said, the changes added in C99 aren't too numerous and are worth knowing about; I'd say learn from the second edition book if that's where you want to start from, and then learn the C99 stuff from the internet.

I think that's all true, but as I said I don't use much C as I do most of my stuff in C++/Java, so sorry if I made any mistakes.

icystorage

Jollibee19343 Posts

August 03 2012 12:13 GMT

#3052

+ Show Spoiler +

sample.lex

/*  
 */ 
 
%{ 
#include <stdio.h> 
#include "y.tab.h" 
extern YYSTYPE yylval; 
%} 
 
%% 
[()]*    yylval=strdup(yytext); return STRING; 
check			return CHECK; 
%%








sample.y

%{ 
#include <stdio.h> 
#include <string.h> 
#include <string.h> 
 
 
#define YYSTYPE char * 
 
  
void yyerror(const char *str) 
{ 
        fprintf(stderr,"error: %s\n",str); 
} 
  
int yywrap() 
{ 
        return 1; 
}  
 
main() 
{ 
	yyparse(); 
} 
 
 
%} 
 
%token STRING 
%token CHECK 
 
%% 
commands: /* empty */ 
        | commands command 
        ; 
 
command: 
        binary 
        ; 
 
binary: 
        CHECK string1 
        { 
		 
                printf("\tSTRING is :%s\n",$2); 
        } 
        ; 
 
string1: 
        STRING 
        { 
                $$=$1; 
	} 
	;

can i ask for some help about flex and bison?
its actually homework but i just got stuck here =/ i want the program to accept a string and its reverse. like a palindrome.
ex. (())))((

but so far all i can do is just output the input string. =/ do you guys have any tips on how should i proceed?

EDIT: btw my production rules are

s -> (s(,
s -> )s),
s -> (blank) but i cannot somehow understand how to code it =/

Craton

United States17247 Posts

August 04 2012 02:11 GMT

#3053

There seems like a better way to write this: http://sqlfiddle.com/#!4/51e32/3

It's possible that query's a result of these painkillers just being really good.

Execution Plan:
+ Show Spoiler +

This is just some little thing I've got running locally and my DB design is kinda mediocre because it suffices for how I use it, but it still seems there should be a "better" way.

supereddie

Netherlands151 Posts

August 04 2012 09:04 GMT

#3054

You might want to add primary key on CHAMPION_ALIASES and SUMMONERS and then use foreign keys in MATCH_HISTORY.

The query itself looks fine to me. Maybe you can use inner joins for CHAMPION_ALIASES as well if you know they always exists and there always are 10.

EruIluvatar

Germany2 Posts

August 05 2012 15:12 GMT

#3055

@DumJumJmyWum and SgtCoDFish

Thank you for your responses. I will order the book in the next days.

Craton

United States17247 Posts

August 05 2012 21:23 GMT

#3056

On August 04 2012 18:04 supereddie wrote:
You might want to add primary key on CHAMPION_ALIASES and SUMMONERS and then use foreign keys in MATCH_HISTORY.

The query itself looks fine to me. Maybe you can use inner joins for CHAMPION_ALIASES as well if you know they always exists and there always are 10.

Can't do Inner joins because the fields can be null in MATCH_HISTORY.

It just seems really weird to do it with so many joins, but I guess it's just because of how I set things up.

tec27

United States3696 Posts

August 05 2012 22:04 GMT

#3057

On August 06 2012 06:23 Craton wrote:

Show nested quote +

Can't do Inner joins because the fields can be null in MATCH_HISTORY.

It just seems really weird to do it with so many joins, but I guess it's just because of how I set things up.

Pretty necessary if you're going to normalize it out like that, I think. You could do it in 2 separate queries (query for all the aliases from match history, then build a list and do an IN ( alias1, alias2, ... , aliasN ) in the second query), but you wouldn't really be saving execution time. You would, however, gain the ability to cache the alias information separately from the database and match history, which is valuable.

JeanLuc

Canada377 Posts

August 06 2012 05:01 GMT

#3058

Hi guys,

I was hoping people who are studying C/C++ could help me with this. I have come back to C++ from a long sojourn learning "easier" languages such as Java, C#. My understanding of C++ was never that great, but I find myself confused about a lot of stuff. In this bit of code I tried writing a version of the common join() function you see in a lot of languages: basically, you give an array of strings to join() and it returns a string of the concatenated elements separated by a delimiter. What I have here seems to work but I have a bunch of questions to ask:

+ Show Spoiler +

//join.cpp
#include "join.h"
#include <iostream>
#include <cstring>
using namespace std;

int main(){
char * arr[]={"Yo","Adrian!","I","Did","It!","said","Rocky"};
char delimiter=',';

const char * phrase=join(arr,delimiter,sizeof(arr)/sizeof(char *));
cout<<phrase<<endl;
if(phrase!=NULL)
delete [] phrase;

}

const char * join(char * arr[], char delimiter, int words){
char * str;
int len=0;
int a=0;
for(int i=0; i<words; i++){
len+=strlen(arr[i])+1;
}
str=new char[len];
for(int i=0; i<words; i++){
for(int j=0; j<strlen(arr[i]); j++){
str[a++]=arr[i][j];
}
if(i<(words-1)) str[a++]=delimiter;
}
str[a]='\0';
return str;
}

One thing I'm curious about is.. whether the memory allocation/deallocation in this is handled OKAY. Is there a way to determine the length of the array of char pointers within the function so I don't need to pass that as a parameter? Is it necessary that the function return a const char *?

And basically, if you're so inclined, please bash this code and tell me why its noob (somethign which I intuit it to be). Thanks for any help you can offer.

Craton

United States17247 Posts

August 06 2012 08:01 GMT

#3059

Another question using the same database from before.

In one of my views I'd like to have a column denoting "streaks," where a streak is defined consecutive wins or losses. What I'd like to do is basically take my list if games, sort it by MHID descending, and then have some kind of SQL that will say there have been X many of this result in a row.

MHID are entered in such a way that a higher number denotes a more recent game, but may not be consecutive.

My thought was that I could achieve this by some kind of CONNECT BY logic, but I can't figure it out (I seemingly keep getting infinite loops with the logic I've tried).

I also tried LEAD and LAG but couldn't quite get there.

End result would look something like this:

MHID -- RESULT -- STREAK
9 -- LOSS -- 1
8 -- WIN -- 3
6 -- WIN -- 2
1 -- WIN -- 1

Abductedonut

United States324 Posts

August 06 2012 09:12 GMT

#3060

On August 06 2012 14:01 JeanLuc wrote:
Hi guys,

I was hoping people who are studying C/C++ could help me with this. I have come back to C++ from a long sojourn learning "easier" languages such as Java, C#. My understanding of C++ was never that great, but I find myself confused about a lot of stuff. In this bit of code I tried writing a version of the common join() function you see in a lot of languages: basically, you give an array of strings to join() and it returns a string of the concatenated elements separated by a delimiter. What I have here seems to work but I have a bunch of questions to ask:

+ Show Spoiler +

Your code is fine, for the most part. Your memory alloc/dealloc is fine, although, why keep arr around?
Really memory alloc/dealloc depends on the program. But yeah, yours is fine.

To answer your question, no, there's no way to find the size of an array in the traditional way you do in Java/C#. Although, you can use some ghetto tricks like ALWAYS ending the last element of the array in a word or int or whatever and searching for that in your function to find the answer. That's just C/C++, man.

To answer whether or not you HAD to declare it const, the answer is no. Const just basically means that the compiler should not alter the value. So if you did something like:
join(arr,delimiter,sizeof(arr)/sizeof(char *))[1] = 'a';

It will give you a compiler error, saying you're writing to read-only. Whereas, declaring it as just a char could potentially lead to a crash if you fired that same code. But otherwise, not too much to worry about there.

Here's something to bash your code. Declaring arr as:
char *arr[]= {"Yo","Adrian!","I","Did","It!","said","Rocky",NULL};

Leads to a NULL pointer dereference which could potentially allow a hacker to control flow of execution in your program by Mapping address 0 to a pointer that points to a function of his choice. Alternatively, it can be used to crash your program. Not very good if it's a anti-virus

Happy Programming!

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