Retrieve and store elements (according to conditions) from an array.

Answer 1

Another try:

void applyThingy(int *grid, int xPitch, int yPitch)
{
    int row, column;
    int *rowPointer = grid;

    for(row = 0; row < 3; ++row)
    {
        int *columnPointer = rowPointer;

        for(column = 0; column < 3; ++column)
        {
            doOperation(columnPointer);
            columnPointer += xPitch;
        }

        rowPointer += yPitch * 9;
    }
}

applyThingy(&grid[SUB(n)], 1, 1); // Perform on 3x3 subgrid
applyThingy(&grid[ROW(n)], 1, 0); // Perform on row
applyThingy(&grid[COL(n)], 0, 1); // Perform on column

Answer 2

I'm not sure what you want to do, but is it something like this?:

#define IDX(row, col) ((row)*9+(col))

int m = some_column;
for (int n = 0; n < 9; n += 3) {
  a = grid[IDX(n, m)];
  b = grid[IDX(n+1, m)];
  c = grid[IDX(n+2, m)];
  r = ...;
  ...
}

Also, I'm not sure what you want to do with your operation

r = ((a = ~a) & (b = ~b)) | ((b | a) & ~c);

You're assigning ~a to a, is that what you want? How is a defined, and what are you trying to set it to? What are you trying to achieve?