Spiral using ncurses

I tried to write a program to draw a spiral using the ncurses library - one which draws slowly in a way which can be seen noticeably. I first analyzed the number of characters to be drawn in each direction - down, right, up and left.

I prepared a table having the number of characters in the outer spiral of the spiral design. I used a variable, m, to hold the number of characters in a particular direction. I programmed m to change according to the mathematical pattern which we can notice in the table.

+----------+----+-----+------+--------+
| n        |  1 |   2 |   3  |    4   |
| down     |  4 |   8 |   12 |   16   |
| right    |  3 |   7 |   11 |   15   |
| up       |  2 |   6 |   10 |   14   |
| left     |  1 |   5 |   9  |   13   |
+----------+----+-----+------+--------+

I leave the code for the interested reader here. I implemented this using C with the help of the ncurses library for moving the cursor in the relevant directions before printing the character.

#include <curses.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char* argv[])
{
 int x, y, n, i, m, dx, dy, j;
 int ay[] = {1, 0, -1, 0};
 int ax[] = {0, 1, 0, -1};
 int am[] = {1, 1, 1, 1};

 char s[80];

 n = atoi(argv[1]); 
 m = n * 4;

 initscr();
 cbreak();
 noecho();
 nonl();
 intrflush(stdscr, FALSE);
 keypad(stdscr, TRUE);

 x = 0;
 y = 0;

 while (m > 0)
 {
  for (i = 0; i < 4; ++i)
  {
   dx = ax[i];
   dy = ay[i];
   for (j = 0; j < m; ++j)
   {
    x += dx; y += dy;
    mvaddstr(y, x, "X");
   }
   system("sleep 1");
   refresh();
   --m;
  }
 }

 system("sleep 1");

 endwin();

 return 0;
}

The program, when run, should draw the pattern arm by arm or the spiral, i.e, first downward, then rightward, then upward and then leftward. The following is the output for n = 3:

X
X XXXXXXXXXX
X X        X
X X XXXXXX X
X X X    X X
X X X XX X X
X X X  X X X
X X XXXX X X
X X      X X
X XXXXXXXX X
X          X
XXXXXXXXXXXX