#include <stdio.h>
#include <stdlib.h>
int main()
{
  /* imatrix is a pointer to a pointer to an int */
  
  int **imatrix;

  int numrows;
  int numcols;
  int row, col;

  numrows = 4;
  numcols = 4;

  /*
   * Allocate space for pointers to the rows
   *  The pointer to row 0 is imatrix[0]
   *  The pointer to row 1 is imatrix[1]
   *  etc.
   *
   * Always check return value from malloc,
   * and always call free() for everything
   * that malloc() gives you (after you are
   * through with it, of course).
   *
   */

  imatrix = malloc(numrows * sizeof(int *));
  if (!imatrix) {
    printf("Error allocating %d bytes for imatrix\n", numrows * sizeof(int *));
    return 0;
  }
  else { /* you don't really need to print this, but just to see: */
    printf("Allocated %d bytes for imatrix\n", numrows * sizeof(int *));
  }

  /* 
   * Now, for each row, allocate space for
   * the matrix columns
   * the pointer to the first  column of row 0 is imatrix[0][0]
   * The pointer to the second column of row 0 is imatrix[0][1]
   * etc
   *
   */


  for (row = 0; row < numrows; row++) {
    imatrix[row] = malloc(numcols * sizeof(int));
    if (!imatrix[row]) {
      printf("Error allocating %d bytes for imatrix[%d]\n", 
              numcols * sizeof(int), row);
      for (; row-1>= 0; row--) {
        free(imatrix[row]);
      }
      free(imatrix);
      return 0;
    }
    else { /* you don't really need to print this, but just to see: */
      printf("Allocated %d bytes for row number %d\n", 
              numcols * sizeof(int), row);
    }
  }

  /* 
   * Here is a loop that stores different values in each element
   */
  for (row = 0; row < numrows; row++) {
    for (col = 0; col < numcols; col++) {
      imatrix[row][col] = row * numcols + col;
    }
  }

  /*
   * Now, print out the matrix
   */
  for (row = 0; row < numrows; row++) {
    for (col = 0; col < numcols; col++) {
      printf("matrix[%d][%d] = %d\n", row, col, imatrix[row][col]);
    }
  }
  return 0;

  /* now free up everything that malloc() gave you */
  for (row = 0; row < numrows; row++) {
    free(imatrix[row]);
  }
  free(imatrix);

}