Question

I am currently using the following code to get the current row and column of an element in a 2D int array:

const int num_rows = 5;
const int num_columns = 7;

int a[num_rows][num_columns];

int *p = &a[2][4];

int row = (p - &a[0][0]) / num_columns;
int col = (p - &a[row][0]);

This works fine but now I need to change the code to take the number of rows and columns as a parameter. As far as I know, this means I need to create the 2D array dynamically:

int** ary = new int*[sizeX]; 

for(int i = 0; i < sizeX; ++i) 
    ary[i] = new int[sizeY]; 

If I create the 2D array this way, the above code to find the row/column breaks. What can I do?

Answer 1

 int *ary = new int [sizeX * sizeY]; // allocate memory for the 2d array

 for(int i = 0; i < sizeX; ++I)
     for(j = 0; j < sizeY; ++j) 
          ary[i * sizeY + j] = 0;

  // to get the value of collumn c and row r: use ary[c * sizeY + r];