Re: new vs. vector vs. array

From:

mzdude <jsanga@cox.net>

Newsgroups:

comp.lang.c++

Date:

Fri, 24 Apr 2009 06:13:23 -0700 (PDT)

Message-ID:

<83bc8c75-9f41-4968-bc47-8ab3b11104c4@u8g2000yqn.googlegroups.com>

On Apr 24, 3:26 am, "Mark S." <markstar.n0s...@hotmail.com> wrote:

Hi,
even though I'm still at the beginning of my learning process, I am
anxious to program something "real". So I would like to write a little
program to solve Sudokus with variable dimensions (n*n). I think I have
a pretty good idea about the algorithm, but since you guys here strongly
suggested to avoid new & delete as much as possible, I was wondering how
you would suggest how I store the classes:

Basically, I think I need a class to store the dimensions of the field
which points to the n*m elements (with their own class). I thought I
would do something like this:

class Element {
public:
        Element(int i = 0); // 0 means no number
        // more variables to store status, etc.

}

class Field {
        /* I don't know how to get any of these to work */
        vector<Element> e || Element e[][] || Element* e // ??=

public:
        Field(int x = 1);
        // functions to solve the Sudoku

};

The problem is that I don't know how to deal with multidimensional
vectors or arrays. I was thinking of using a single vector which is n*n
big. Of course, I would have to convert the numbers then (eg. for 3*3,
[1][1] would become [3]). Moreover, this solution does not seem very
elegant to me.

So, what would you recommend? An array of pointers to the elements? A
vector of pointers? Or a vector of the elements themselves?

Thank you in advance!
        Mark

P.S.: I have used Google, of course, but I did not get any of these to wo=

rk:

*[1]* Array (uses 'new' so maybe not recommended?):
This works in main():
        const int n = 3;
        int (*np)[n] = new int[n][n];
        np[2][3] = 4;

However, I don't get it to work in my class (I know that the syntax is
wrong, but I don't know what the correct one is):
        class Field {
                const int n; // field dimensions
                int x, y; // subsection dimen=

sions

                int (*fp)[];
        public:
                Field(int x = 1);
        };

        Field::Field(int i) : n(i) {
        // { calculate subsection }
                fp = new int[n][n];
        }

*[2]* Vector:
I only know it's something like
        vector< vector<Element> > f;
But I wouldn't even know how to push The elements to the right row, let
alone how to do this through a class.

typedef std::vector<int> Columns;
typedef std::vector<Columns> Sodoku;
int main()
{
   int n = 9;
   int m = 4;
   Sodoku s = Sodoku( n, Columns(m));

   s[3][1] = 4;
}