// testing 2D array access using a pointer
//
#include <stdio.h>

int main( void)
{
  int a[3][4]; // = { {1,2,3,4}, {5,6,7,8}, {9,10,11,12} }; // 2D array, on stack

  for( int row = 0; row < 3; ++row) {
    for( int col = 0; col < 4; ++col) printf( " %3i", a[row][col]);
    putchar('\n');
  }

  int *p = &a[0][0]; // pointer to first element

  for( int i = 0; i < 12; ++i) printf( " %3i", p[i]);
  putchar('\n');

 // p[row*4+col] is the same as a[row][col] for 2D array with 4 columns
 //
  for( int row = 0; row < 3; ++row) {
    for( int col = 0; col < 4; ++col) printf( " %3i", p[row*4+col]);
    putchar('\n');
  }
  
}
   
/* sample run:

   1   2   3   4
   5   6   7   8
   9  10  11  12
   1   2   3   4   5   6   7   8   9  10  11  12
   1   2   3   4
   5   6   7   8
   9  10  11  12
*/