C++ 2D array to 1D array

Question

I am attempting to convert a 2D array to 1D. I\'m extremely new to C/C++ but I think it\'s very important to learn how to convert a 2D array to 1D. So here I am stumbling u

Answer 1

http://www.cplusplus.com/doc/tutorial/arrays/

In that link look at the section on pseudo-multidimensional arrays.

I've seen many examples that that get the subscripting algorithm wrong. If in doubt, trace it out. The order of sub-scripting a 2D array should go sequentially from 0-(HEIGHT*WIDTH-1)

#define WIDTH 5
#define HEIGHT 3

int jimmy [HEIGHT * WIDTH];
int n,m;

int main ()
{
  for (n=0; n<HEIGHT; n++)
    for (m=0; m<WIDTH; m++)
    {
      jimmy[n*WIDTH+m]=(n+1)*(m+1);
    }
}

Answer 2

You are right with your supposition:

The cycle should be like:

for (q = 0; q < n; q++)
{
    for (t = 0; t < m; t++)
    {
        b[q * m + t] = a[q][t];
    }
}

It is always easier to consider such conversions from the view point of the higher dimension array. Furthermore with your code you did not actually modify i or j in the b assigning cycle, so you should not expect different values to be assigned to the different array members of b.

Answer 3

First of all, the size of the 1D array should be n*m.

The cycle can be as follows-

int lim = n*m;

for(q = 0; q<lim; ++q) {

    b[q] = a[q/m][q%m];
}

Answer 4

This code

int n=0,m=0; // 2D array nRow, nCol
int a[n][m];

is invalid. First of all the dimensions shall be constant expressions and there is no sense to set them to 0.

And the more simple way to do your task is to use pointer. For example

int *p = b;

for ( const auto &row : a )
{
    for ( int x : row ) *p++ = x;
}