Thread: Changing from one dimensional arrays to two

I want to take the entries of a one diemsional array that is 1 X a*b in size and transfer them into two dimesional array that is a X b in size. The problem is that I am pretty new to C. I am simply trying to use it for a project in statistics. I am familiar with basic loops and such, but basically I have only one semester of programming experience.

Thanks for any tips anyone can give me.

Dean

Try this:

Code:

/**
 * make2d: takes an array of integers and returns a 2-dimensional array
 *         of integers with specified number of rows and columns.  Allocates
 *         a new array, so you must remember to free it after use.
 */
int** make2d(int* flatArray, unsigned int numRows, unsigned int numCols)
{
    int** retArray(NULL);
    unsigned int i, j;

    if( NULL != flatArray )
    {
        retArray = (int**) malloc(sizeof(int*) * numRows);

        for( i = 0; i < numRows; i++ )
        {
            retArray[i] = (int*) malloc(sizeof(int) * numCols);
            for( j = 0; j < numCols; j++ );
            {
                retArray[i][j] = flatArray[i * numRows + j];
            }
        }
    }

    return retArray;
}

Does that make sense? It's been a while since I last wrote regular C, so I might be using some unsupported syntax, but I think that does what you're asking. A few caveats are that if you give it an array that isn't as big as the specified size (numRows * numCols), it'll segfault. Also, you have to remember to free the array returned after you're done, otherwise it'll be a memory leak.

Does this work? Note that I willl always know the value of nrows and ncols beforehand. I'm just looking for something that will move a list of numbers (one dimensional) to a table of numbers (two dimensional) in a way that fills the table from top to bottom, right to left.

Code:

double onedim[nrows*ncols+1]
double twodim[nrows+1][ncols+1];
int i, j, k;

k=1;

for(j=1 ; j<=ncols ; j++)
        for(i=1 ; i<=nrows ; i++)
                {
                 twodim[i][j]=0.0;
                 twodim[i][j]=onedim[k];
                 k++;
                 }

Thanks guys (and girls).