dynamic arrays

**laserlight** · 05-12-2008

that means to put a for loop on the 2nd pointer and another for loop for the 3rd pointer and another for loop for the nth pointer yes?

Yes. Note that you could also use a one dimensional array to represent a multi-dimensional array, upon which you would calculate the index offsets yourself.

I would have thought C would be a pre-requisite for a C++ course?

No, at least not for the courses taught by Andrew Koenig and Barbara Moo, but then they teach vectors before dynamically allocated arrays.

EDIT:
Oh, and I was taught C++ without a C pre-requisite, though they taught me the C legacy of C++ (but with I/O streams) before the C++ specific stuff, somewhat like sokermaniac's professor's approach.

**sokermaniac** · 05-12-2008

ok for a 2d here is what i have:

int **board;

int rows;
int columns;

cout << "Enter number of rows and columns: ";
cin >> rows >> columns;

board = int int* [rows];

for (int row = 0; row < rows; row++)
board[row] = new int[columns];

return 0;

something from an example i had.

**medievalelks** · 05-12-2008

Originally Posted by cpjust

Strange... I would have thought C would be a pre-requisite for a C++ course?

Sadly, it not only seems to be pre-req, but "C with Classes" seems to be what most college grads in the US and abroad are bringing to the workplace. I'd be hard pressed to find a beginner that doesn't make the same mistakes that have been made for years, instead of simply doing things the "C++ way".

**sokermaniac** · 05-12-2008

yeah for my class you can dive right into C++ without C. I'm assuming i may have to learn C sometime eh?

**Elysia** · 05-12-2008

Originally Posted by sokermaniac

ok for a 2d here is what i have:

int **board;

int rows;
int columns;

cout << "Enter number of rows and columns: ";
cin >> rows >> columns;

board = int int* [rows];

for (int row = 0; row < rows; row++)
board[row] = new int[columns];

return 0;

something from an example i had.

Please use code tags, but yes, you're on the right track. You just need to add another dimension there.

**laserlight** · 05-12-2008

ok for a 2d here is what i have:

Looks okay, though you might want the array index to be an unsigned int instead of an int. Also, remember to delete[] what you new[].

**cpjust** · 05-12-2008

Originally Posted by medievalelks

Sadly, it not only seems to be pre-req, but "C with Classes" seems to be what most college grads in the US and abroad are bringing to the workplace.

Or as I call it -- C+ programming.

I learned C by myself, followed by C++, so I'm not sure how they structure the courses. But I guess there are pros & cons to learning C first.
Pro: You can learn the language basics without being overwhelmed by classes, STL, templates...
Con: When you do learn C++ it might take longer to unlearn some of the ugly C stuff.

**Elysia** · 05-12-2008

I would like to say that everyone drops C and starts learning C++ and C++/C (my own abbreviation for C code compiled with a C++ compiler

).
Obviously, working with pointers and all that might be called C, but it is definitely good knowledge! :O

**sokermaniac** · 05-12-2008

ok sorry about not using code tags :P not used to forums haha. 2nd my prof was going to start delete but toward the end of the semester he decided not to teach that part but im sure its not difficult to use or learn. then again im a slow learner. :P 3rd how come you would want it to be an unsigned int? is it because the dimensions or the data may be negative?

Code:

int **board;

int rows;
int columns;

cout << "Enter number of rows and columns: ";
cin >> rows >> columns;

board = int int* [rows];

for (int row = 0; row < rows; row++)
board[row] = new int[columns];

return 0;

for a 3d

Code:

int ***board;

int rows;
int columns;
int thirddim;

cout << "Enter number of rows and columns and some number for the 3rd dimeninsion: ";
cin >> rows >> columns >> thirddim;

board = int int* [rows];

for (int row = 0; row < rows; row++)
board[row] = new int[columns];
for (int  column = 0; column < columns; column++)
board[colum] = new int[thirddim];

return 0;

**sokermaniac** · 05-12-2008

by the way, i really appreciate everybody helping me out here! i like programming but im no stud compared to you all! its a constant struggle with me

**Elysia** · 05-12-2008

Now that you are using code tags, you can actually indent the code and the board won't strip away the spaces! You should try doing that.
Secondly, delete is very important and I can't believe someone would not teach it >_<
Anything allocates with new will never go away unless you call it with delete.
Anything allocates with new must be deallocated with delete.
Anything allocated with new [] (such as your array), must be deallocated with delete[]. Otherwise you're going to leak memory (memory will still stay as used, but you can't access it).

And as for your code... well, you seem to have a small problem.
An array (pointer) to hold a pointer to another array (pointer) to hold more pointers to more arrays.
Try writing it down on paper, maybe. You'll see what's wrong. Hopefully anyway.
Remember that only a pointer can contain an address, and to contain a pointer to a pointer, you need a pointer to pointer (type**). This goes up.

**sokermaniac** · 05-12-2008

yeah my prof is a little unorthodox. but i had no choice but to get him this semester. i've been reading ahead and im understanding the delete concept just not how to use it haha.

and the small problem. did i need to initalize board again for the 3rd d for the 2nd for loop?

**Elysia** · 05-12-2008

3rd array holds normal ints.
2nd arrays must hold pointers to that array of int (thus int*).
1st array must hold pointers to the 2nd array which holds int* (the type then becomes...?)

**sokermaniac** · 05-12-2008

something like this?

Code:

int ***board;

int rows;
int columns;
int thirddim;

cout << "Enter number of rows and columns and some number for the 3rd dimeninsion: ";
cin >> rows >> columns >> thirddim;

board = int int* [rows];

for (int row = 0; row < rows; row++)
     board[row] = new int[columns];
for (int  column = 0; column < columns; column++)
     board[row][column] = new int[thirddim];

return 0;