Recursion function and pass by reference

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Hello

I have this program working with the commented version. But that is just my way to do it. The tutorial wants it done by applying pass by reference.

SO I started modifying it and now I'm a little stuck but almost there.

Can you guys take a look at it and tell me what am I missing here.

Thanks

C++

#include <iostream>
#include <cstdlib> //had to force it becasue my compiler (Code::Blocks) does not contain system.

using namespace std;
/*int n = 1, sum = 0;

int sumDigits(int n, int sum)
{
    //
	if (n == 0)
    {
        return sum;
    }
    else
    {
        // applying recursion and returning the value into the function
        sum = sum + n%10;
		n= n/10;
        return sumDigits(n, sum);
    }
}

int main(int argc, char* argv[])
{
	n = 1, sum = 0;

        cout << "Enter a non-negative integer: ";
        cin >> n;
        sum = sumDigits (n, sum);
        cout << "The sum of all digits "<< n << " is: " << sum << endl;

	system ("PAUSE");

        return 0;
}
*/

int sumDigits(int &);

int main()
{
	int n;
	sumDigits(n);
}

int sumDigits(int &n)
{
    cout << "Enter a non-negative integer: ";
    cin >> n;
        if (n == 1)
        {
            return 1;
        }
        else
        {
            return (n - 1) + n;
        }
    cout << "The sum of all digits "<< n << " is: " << n << endl;


	system ("PAUSE");

        return 0;
}

Posted 10-Jun-13 7:56am

lotussilva

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Comments

Sergey Alexandrovich Kryukov 10-Jun-13 14:03pm

"Tutorial wants..."? You personification in a kind of your figure of speech went too far. A tutorial does not "want" anything". Your post cannot make sense until you explain what do you want to achieve. And why passing by reference + recursion, without foolishness? I don't say you cannot do it, I'm asking why.
—SA

Sergey Alexandrovich Kryukov 10-Jun-13 16:07pm

Please see my comment to my answer.
—SA

2 solutions

Solution 1

You can use passing by reference, of course, but first look at my comment to the question.

The code (not commented) you provided, has two blocker problem: 1) n is not initialized before the first call; 2) there is no recursion at all.

Keep thinking. Even if I wanted to give you a complete solution, I could not, because your post does not contain the real specifications, and none of the existing code does not provide unambiguous description of what do you want to achieve. Formally, this is not even an acceptable approach to asking questions. Even if you assumed that your code should be considered as a correct spec for the problem, you cannot rely on it, because it's not known if this code is correct or not. It does suggest that the problem is to sum all the decimal digits in some previously number, so…

…if the assumption above is correct, the other problem of the code (not commented out) is: 3) the method sumDigits contains input in it; it shouldn't.

—SA

Posted 10-Jun-13 8:15am

Sergey Alexandrovich Kryukov

Comments

Sergey Alexandrovich Kryukov 10-Jun-13 14:35pm

Help who?! I personally don't need any help, but it looks like you do.

You haven't added much with this comment. This does not spec the problem. This is not too bad, but it's bad that you don't understand it.
Besides, your item statements don't look correct. For example, "value is passed by reference" is an apparent oxymoron. :-)

I just don't want to give you an answer. If you won't overcome very basic issues by yourself, consider the goal of an exercise is completely defeated.

—SA

Sergey Alexandrovich Kryukov 10-Jun-13 16:05pm

OK, you have to understand some things. You need help, and I provide this help. You are the student who is supposed to solve some problem by yourself, without any help. Is that so?

However, we all realize that some people can have some particular problem in some cases, so we are trying to help, even is such cases. But it looks like "rude" for you means simply the idea that people are not doing all your work for you, that would be plain cheating. Will you call your professor "rude" for an insufficient mark on your exam? Or some cases like that? But that professor get some salary to teach you. Here, you are getting help from qualified people for free. And yet, you think you can call "rude" something which you don't like. Isn't that merely because you post here as anonymous? Is so, you are rude, and shameless.

With such attitude, you cannot hope to be welcome here. You don't even take the labor to help us to help you.

And let me decide by yourself where to comment and where not. I won't ask if you want some help from me or not. I can write what I think is right, no more, no less.

Thank you for understanding.
—SA

CPallini 10-Jun-13 16:22pm

My 5.

Sergey Alexandrovich Kryukov 10-Jun-13 16:25pm

Thank you, Carlo.
—SA

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

CPallini · Accepted Answer · 2013-06-10T09:18:00

Solution 2

C++

void sum_digits(int & n, int & sum)
{
  if ( n == 0 ) return;
  sum += n % 10;
  n /= 10;
  sum_digits(n, sum);
}

#include <iostream>
using namespace std;

int main()
{
  int n, sum=0;
  cout << "enter a non-negative number" << endl;
  cin >> n;
  if ( n < 0 ) return -1; // don't trust the user
  sum_digits(n,sum);
  cout << "sum is " << sum << endl;
}

Posted 10-Jun-13 9:18am

CPallini

Comments

lotussilva 10-Jun-13 15:53pm

Thank you CPallini. This makes a lot more sense to me. It's a little similar to my first design. But definitely cleaner. However, I'm a little raw at Cpp, and this may be a stupid question, but where is the pass by reference in your solution? I just wanna identify it if it's there.

Sergey Alexandrovich Kryukov 10-Jun-13 16:24pm

Don't get me wrong: your question wasn't really stupid, otherwise I would not answer. It only should have been more comprehensively formulated...
—SA

CPallini 10-Jun-13 16:29pm

C++ language specifies parameter passing by reference with the ampersand operator ('&') in the function definition (and declaration). I believe you now can see it.

lotussilva 10-Jun-13 16:43pm

Of course! Lol. Right in front of my face! Thank you. I do see it!

edit...

I just got home and rechecked your code and it looks like I wasn't too far from the right answer. All I needed was to add the ampersand in the parameters. But Help you for helping me see it clearer.

Sergey Alexandrovich Kryukov 10-Jun-13 16:09pm

My 5, but I would not answer OP like that; this person has wrong attitude; please see the comments to my answer and comment; besides, it looks like a school assignment, it's not fair to provide a complete solution.
—SA

CPallini 10-Jun-13 16:23pm

Basically I agree with you, but, sorry, I couldn't help it.

Sergey Alexandrovich Kryukov 10-Jun-13 16:25pm

I understand you of course, no need to be sorry... :-)
—SA

Sergey Alexandrovich Kryukov 10-Jun-13 16:23pm

One note: first parameter in sum_gidits should be by value. Will you modify it?
—SA

CPallini 10-Jun-13 16:27pm

Nope: the function is intended to use it that way (I don't know the OP actual requirements, so I designed the function to use both parameters by reference, meaningless as it could be).

Sergey Alexandrovich Kryukov 10-Jun-13 16:40pm

Ah, I got it now: you carry the position of the digit, also reduce it to recursion instead of having a loop. Not optimal, but does illustrates the technique... :-)
—SA

lotussilva 10-Jun-13 16:41pm

Sergey, I am a software engineer graduated from park University with focus on Web Development. I'm also the owner of LOTUS Marketing Solutions. My name is Luis Silva. No, this is not a school assignment. It's a tutorial. I've programmed in cpp, but very little.

Sergey Alexandrovich Kryukov 10-Jun-13 16:52pm

OK, thank you for this information. Sorry for calling you a student, but this is the impression from the "requirements" which look like the just for the study. Maybe you are a self-teaching student, as you mentions some tutorial (which I cannot get; what's "tutorial wants")? You see, in real development, the problem should be be posed like that. The effective and clear solution for such problem is: only one parameter, n on input, value-type, no recursion, shifting decimal digit position in a loop. Recursion here is not effective and much less readable.

(It is a well-recognized and described in literature fallacy of many programming manuals: they teach how to use recursion, technically correctly, but they fail to teach how to design the code with recursion in the way it really makes sense. One typical illustration of recursion is factorial function: it's often used to explain recursion, but in fact, recursion is very inefficient and can even cause stack overflow; and the loop solution is way better. You example is still better than that.)

—SA

CPallini 11-Jun-13 2:33am

(about teaching recursion) Wirth's "Algorithms + Data Structures = Programs" (1976) is an exception.

Sergey Alexandrovich Kryukov 11-Jun-13 6:52am

Aha...
—SA

lotussilva 10-Jun-13 17:00pm

Standing ovation! There you Sergey! I knew you had it in you! Do you see how different this response is compared to the way you responded first? I appreciate this. And it was informative! Thank you for extending the courtesy. All is well again

Sergey Alexandrovich Kryukov 10-Jun-13 18:09pm

Thank you, Luis. I don't think I did anything wrong in first place though. I want to help people who are going to really use the help, and then I'm ready to put decent effort in such cases. I appreciate your openness and open mind you demonstrated. No problems, of course.
—SA

Recursion function and pass by reference

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Recursion function and pass by reference

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