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Trying to understand... Posted by Deele on 31 May 2007 at 2:55 AM

I am analyzing a C++ console based program but I am very newbie to C++ and I want to learn it. Main reason, why I am analyzing this code, becouse I need to remake it by myself but in form of MFC dialog.
Okay, I have couple of questions and I hope, someone will help me...
1) Does this one makes an array? If so, then, all the array values from 1..32 will be empty, if I call set[1] or any other?

int set[32]

2) What will I get, when I will call just: "set", not "set[n]" ?

3) What will I get, when I will say "set+k" if:

int k=0;

4) What is doing this loop? I know that "EOF" is EndOfFile that is CTRL+Z, but what this loop does?

while (k<32 && scanf("%d",set+k)!=EOF) k++;

5) What is doing here:

for (i=0;i<k-1;i++) printf("%d,",set[i]);

6) What this will "set[k-1]" print out?

if (k) printf("%d",set[k-1]);

Okay, (not a)full code, if you ask, is here:

int main(void) /*demo*/
{
	int set[32],i;
	int k=0;

	printf("enter the set elements separated by blanks and ctrl-z at the "
	"end\n");

	while (k<32 && scanf("%d",set+k)!=EOF) k++;
	printf("your set:\n{");
	for (i=0;i<k-1;i++) printf("%d,",set[i]);
	if (k) printf("%d",set[k-1]);
	printf("}\n");
	printf("its subsets:\n");
	subsets(set,k);
	return 0;
}

I will have a couple of more questions later on...

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Re: Trying to understand... Posted by bilderbikkel on 31 May 2007 at 3:00 AM

Some quick answers that time permits me:

: 1) Does this one makes an array? If so, then, all the array values
: from 1..32 will be empty, if I call set[1] or any other?
:

: int set[32]

:
Yes, that declares an array with 32 uninitialized values, i.e. these values can be anything.

: 2) What will I get, when I will call just "set", not "set[n]"?
You get the address of the array. 'set' is also equal to '&set[0]'. '*set' is equal to 'set[0]'.

: 3) What will I get, when I will say "set+k" if:
:

: int k=0;

:
The adress 'k' spaces beyond 'set', i.e. '&set[0]+k' (is equal to '&set[k]').

: 5) What is doing here:
:

: for (i=0;i<k-1;i++) printf("%d,",set[i]);

:
Prints the array 'set'

See ya,
bilderbikkel

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Re: Trying to understand... Posted by Deele on 31 May 2007 at 3:29 AM

Cool, I understod almoast everything... Just few more questions in this step:
7) What is meaning of "%d" and "set+k" at "scanf" function? How can I use this in future?

scanf("%d",set+k)

8) What is meaning of "%d" and "set[i]" at "printf" funtion? How can I use this in future?

printf("%d,",set[i])
printf("%d",set[k-1])

9) How to make ending of program just like: "Enter any key to exit..." and only after pushing any key, console window closes?

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Re: Trying to understand... Posted by bilderbikkel on 31 May 2007 at 3:40 AM

: 8) What is meaning of "%d" and "set[i]" at "printf" funtion? How can
: I use this in future?
:

: printf("%d,",set[i])
: printf("%d",set[k-1])

:
'%d' is the placeholder for a value. '%d' denotes that this value is a signed decimal. This value is 'set[i]'

bilderbikkel

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Re: Trying to understand... Posted by Lundin on 31 May 2007 at 3:45 AM

: Cool, I understod almoast everything... Just few more questions in
: this step:
: 7) What is meaning of "%d" and "set+k" at "scanf" function? How can
: I use this in future?
:

: scanf("%d",set+k)

If you write only the array name, in this case "set", it will equal a pointer to the first element in the array. set+k is pointer arithmetics, it means "take the addres of the first element + k elements".
This is the very same as writing &set[k].

In this case, they wanted to assign the value from scanf() to element set[k].

: 8) What is meaning of "%d" and "set[i]" at "printf" funtion? How can
: I use this in future?
:

: printf("%d,",set[i])
: printf("%d",set[k-1])

It means "print element i of the array set". Heh, and it probably also means that you won't understand my reply to 7), to understand pointer arithmetics, you first need to understand arrays.

: 9) How to make ending of program just like: "Enter any key to
: exit..." and only after pushing any key, console window closes?
:

#include <stdlib.h>

and then at the end

system("pause");
return 0;

Or as an alternative:

printf("Press any key to exit");
getchar();
return 0;

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Re: Trying to understand... Posted by AsmGuru62 on 31 May 2007 at 3:46 AM

: Cool, I understod almoast everything... Just few more questions in
: this step:
: 7) What is meaning of "%d" and "set+k" at "scanf" function? How can
: I use this in future?
:

: scanf("%d",set+k)

:

%d in both cases means the formatting specifier. It tells that scanned value from user input (console) will be translated using decimal format, like "1234". set+k mean the address of 'k' element of array 'set'. Note: the address - not the value.

: 8) What is meaning of "%d" and "set[i]" at "printf" funtion? How can
: I use this in future?
:

: printf("%d,",set[i])
: printf("%d",set[k-1])

:

See above for %d - it again tells that value from set[i] must be printed using decimal formatting. set[i] is a value of element indexed by 'i' in array 'set'. Indexes are starting from 0, so the first element of the array is set[0], second - set[1] and so on...

: 9) How to make ending of program just like: "Enter any key to
: exit..." and only after pushing any key, console window closes?
:

printf ("\n\nPress any key to exit...");
getch ();

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Re: Trying to understand... Posted by Lundin on 31 May 2007 at 3:58 AM

:

: printf ("\n\nPress any key to exit...");
: getch ();

:

Noo... don't teach non-standard functions!

getchar();

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Re: Trying to understand... Posted by Deele on 31 May 2007 at 4:06 AM

10) What is doing this loop?

while (k<32 && scanf("%d",set+k)!=EOF) k++;

It is reading an input 32 times searching for EOF? Or what? Every time input is scanned, it is added to set with each loop, increasing "k" by 1? Or what?

PS: Continuing work later...

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Re: Trying to understand... Posted by cactus1 on 31 May 2007 at 5:57 AM

: 10) What is doing this loop?
:

: while (k<32 && scanf("%d",set+k)!=EOF) k++;

:
: It is reading an input 32 times searching for EOF? Or what? Every
: time input is scanned, it is added to set with each loop, increasing
: "k" by 1? Or what?
:
: PS: Continuing work later...
:
It puts a value into set[k], then increments k to get to the next value when the while loop is run again. The !=EOF is to end the while statement midway if the file ends midway.

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Re: Trying to understand... Posted by Lundin on 31 May 2007 at 6:06 AM

It is also a very typical example of why you should use for() loops whenever possible, since the code is hard to read. Here is an improved version that ensures that k has been intialized and ensures integrity of the data stored in "set":

for(k=0; k<32; k++)
{
  int input;

  if(scanf("%d", &input) == EOF)
    break;
  else
    set[k] = input;
}

Note that this example is equally efficient as the original while-loop, both in terms of speed and memory used.

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Re: Trying to understand... Posted by Deele on 31 May 2007 at 11:24 AM

11) If understood right, now, If I want to create "your set" in one variable, I should do this:

int set[32],i;
int k=0;

m_Set = "{";
for (i=0; i<k-1; i++)
{
	m_Set = m_Set + "," + set[i];
}
m_Set = m_Set + "}";

and it will be the same as printed to window:

printf("your set:\n{");
for (i=0;i<k-1;i++) printf("%d,",set[i]);
if (k) printf("%d",set[k-1]);
printf("}\n");

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Re: Trying to understand... Posted by Deele on 1 Jun 2007 at 5:00 PM

Where does everybody gone? Noone cannot help me? 0_o

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Re: Trying to understand... Posted by BitByBit_Thor on 2 Jun 2007 at 3:33 AM

: 11) If understood right, now, If I want to create "your set" in one
: variable, I should do this:

Well... almost. I assume m_Set is defined as CString?
The problem with your code currently is:
1) The first item will look like: "{,1, ...}", and
2) The last item won't be printed.

m_Set = "{";
for (i=0; i<k-1; i++)
{
	m_Set = m_Set + set[i] + ",";
}
if (k > 0) m_Set = m_Set + set[k - 1];
m_Set = m_Set + "}";

Best Regards,
Richard

The way I see it... Well, it's all pretty blurry

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Re: Trying to understand... Posted by Deele on 2 Jun 2007 at 7:30 AM

: : 11) If understood right, now, If I want to create "your set" in one
: : variable, I should do this:
:
: Well... almost. I assume m_Set is defined as CString?
: The problem with your code currently is:
: 1) The first item will look like: "{,1, ...}", and
: 2) The last item won't be printed.
:
:

: 
: m_Set = "{";
: for (i=0; i<k-1; i++)
: {
: 	m_Set = m_Set + set[i] + ",";
: }
: if (k > 0) m_Set = m_Set + set[k - 1];
: m_Set = m_Set + "}";
:

:
: Best Regards,
: Richard
:
: The way I see it... Well, it's all pretty blurry

I got this error (error C2666: '+' : 4 overloads have similar conversions) for line:

m_Set = m_Set + set[i] + ",";

and the same error on line:

if (k > 0) m_Set = m_Set + set[k - 1];

12) What is a main meaning of that "k" (look for program code in earlier posts)? Is it equal to number of set elements?
Ok, at first, there is declaration that "k = 0". Okay. Second, there is loop "while (k<32 && scanf("%d",set+k)!=EOF) k++;". If I analyze this loop:
1> If user is wise, he will enter set correctly that is, for example, set of three chars, seperated with blanks "A B C".
2> Loop is asking if "k" is less than "32". Yes, it is "0". continuing.
3> Loop is setting "set+k" equal to user input. That means, loop is setting "set+k = set[0];" and... "set[0] = A B C;"
4> Loop is asking if that "set[0]" is not equal to "EOF" char. Yes, it is, it is just "A B C". SO, loop continues and adds one to "k" so now "k = 1"
5> Again, we think that user is not a noob :) and will add correctly "EOF" sign "CTRL+Z" at next line and press enter...
6> Loop is asking if "k" is less than "32". Yes, it is "1". continuing.
7> Loop is setting "set+k" equal to user input. That means, loop is setting "set+k = set[1];" and... "set[1] = EOF;"
8> Loop is asking if that "set[1]" is not equal to "EOF" char. No, it isn't, it is "EOF" char. SO, loop stops and continues to next program line...

What this K is for? I think, if I remake this program in dialog way, this "k" will be unnessesary, cause, it will be all the time "k = 0". Am I right?

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Re: Trying to understand... Posted by BitByBit_Thor on 2 Jun 2007 at 9:41 AM

: I got this error (error C2666: '+' : 4 overloads have
: similar conversions) for line:
:

: m_Set = m_Set + set[i] + ",";

:
: and the same error on line:
:

: if (k > 0) m_Set = m_Set + set[k - 1];

:
:

The problem is that the CString class can not convert integer into string.
You'll need to use something like _itoa (integer to ansi) (defined in stdlib), or an equivalent function.

:
: What this K is for? I think, if I remake this program in dialog way,
: this "k" will be unnessesary, cause, it will be all the time "k =
: 0". Am I right?

In the current code the k was used for determining how many elements of set were in use. You will need something equivalent in your program.

Best Regards,
Richard

The way I see it... Well, it's all pretty blurry

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Re: Trying to understand... Posted by Deele on 2 Jun 2007 at 11:51 AM

13) How to convert "int" to "CString"? Is there any other conversition commands?
For example: I have CString called "word" with value "something special" and int called "number" with value "12345". I want to combine "word" with "number" together to get "something special 12345".

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