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Passing a User Define Multidimensional Array

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Join Date: Sep 2008

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gopi17

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Passing a User Define Multidimensional Array

Aug 24th, 2009

hey...i'm having trouble passing a user define 2d array...

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
void genrand(int &game[][],int &size)
{
     int i,j;
     for(i=0;i<size;i++)
     {
       for(j=0;size;j++)
        {
          game[i][j]=(rand()%100);
          }
     }
}
 
int main()
{
    int size;
    int game[][];
    cout<<"Please enter your Game Size";
    cin>>size;
 
    genrand(game[][],size);
 
    return 0;
    system("pause");
}
void genrand(int &game[][],int &size)
{
     int i,j;
     for(i=0;i<size;i++)
     {
       for(j=0;size;j++)
        {
          game[i][j]=(rand()%100);
          }
     }
}
 
int main()
{
    int size;
    int game[][];
    cout<<"Please enter your Game Size";
    cin>>size;

    genrand(game[][],size);
    
    return 0;
    system("pause");
}

This is my code...i read in another c++ forum where they stated that i need to specify the array...i'm not sure either...

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Join Date: Aug 2007

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Reputation: vmanes is a splendid one to behold

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vmanes

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Re: Passing a User Define Multidimensional Array

Aug 24th, 2009

Declaring the array as you're trying to do, you MUST declare the sizes of the row and column dimensions*.

To allow the user to enter the size at runtime, you'll have to use dynamically allocated array, that is, pointers.

Generally speaking, this is the pattern:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
   int **game ;
   int size = 0;
   cin >> size;
   game = new int* [size];
   for( int i = 0; i < size; i++ )
   {
         game[i] = new int  [size];
    }
   int **game ;
   int size = 0;
   cin >> size;
   game = new int* [size];
   for( int i = 0; i < size; i++ )
   {
         game[i] = new int  [size];
    }

This assumes you want a square matrix. If you have differing row and column dimensions, remember that the first allocation is the number of rows, you will set the column size inside the loop.

* - yes, some compilers are now allowing you to allocate array with variables, following the new C standard. It's not C++ standard, yet.

Last edited by vmanes; Aug 24th, 2009 at 3:01 am. Reason: added footnote

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Join Date: Oct 2008

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adatapost

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Re: Passing a User Define Multidimensional Array

Aug 24th, 2009

Here is incorrect syntax. You must have to specify the bounds for all dimensions.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
  int game[][];
  int game[][];

Correct way is,

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
 int game[4][4];
 int game[4][4];

Or use pointer to pointer (dynamic memory allocation). http://www.cplusplus.com/doc/tutorial/dynamic/

Another problem is with calling a function,

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
genrand(game,size); // do not add subscripts
genrand(game,size); // do not add subscripts

Arrays are not passed using operator &, because the name of the array is the starting location in memory of the array.
i.e the name of array is alread a pointer. The name of an array, for example, foo, is equivalent to &foo[0].

Last edited by adatapost; Aug 24th, 2009 at 3:05 am.

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Join Date: Sep 2008

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gopi17

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Newbie Poster

Re: Passing a User Define Multidimensional Array

Aug 24th, 2009

okay, i understand...juz wanna ask...is it possible to create a huge array then minimize the array according to the users input...
for example

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
game[500][500];
then minimize from there...
game[500][500];
then minimize from there...

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niek_e

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Roasting Maven

Re: Passing a User Define Multidimensional Array

Aug 24th, 2009

•

Originally Posted by gopi17

okay, i understand...juz wanna ask...is it possible to create a huge array then minimize the array according to the users input...
for example
Help with Code Tags

C++ Syntax (Toggle Plain Text)
game[500][500];
then minimize from there...
game[500][500]; then minimize from there...

Why on earth would you want to do that?? First you ask your OS to reserve an enormous amount of memory for your program, but then when the user has inputted the real dimensions, the OS can free the useless memory again. That sounds a bit in-efficient doesn't it?

Just use the code that vmanes already posted.
Don't forget to delete[] the memory when you're done with it!

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Join Date: Sep 2008

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gopi17

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Re: Passing a User Define Multidimensional Array

Aug 24th, 2009

hmmm....ic...thanks for the info....
do you mind explaining the code...i don't quite get it...

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
 int **game ;                        <---------This line
   int size = 0;
   cin >> size;
   game = new int* [size];        <---------This line
   for( int i = 0; i < size; i++ )
   {
         game[i] = new int  [size];               <---------This line
    }
 int **game ;                        <---------This line
   int size = 0;
   cin >> size;
   game = new int* [size];        <---------This line
   for( int i = 0; i < size; i++ )
   {
         game[i] = new int  [size];               <---------This line
    }

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niek_e

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Roasting Maven

Re: Passing a User Define Multidimensional Array

Aug 24th, 2009

I could try, but you should probably read this first. I'll the code a lot clearer to you!

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firstPerson firstPerson is offline

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Re: Passing a User Define Multidimensional Array

Aug 24th, 2009

•

Originally Posted by gopi17

okay, i understand...juz wanna ask...is it possible to create a huge array then minimize the array according to the users input...
for example
Help with Code Tags

C++ Syntax (Toggle Plain Text)
game[500][500];
then minimize from there...
game[500][500]; then minimize from there...

I think what you are looking for is vector or this vector

They have the capability of resizing to whatever size you would like
them to be.

The function vector::push_back, add elements to the end of the
vector.

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