Generate a spiral matrix for n elements source code

This snippet submitted by Raza on 2006-09-30. It has been viewed 35724 times.
Rating of 5.7 with 145 votes
#include <stdio.h>

#define UP 1
#define DOWN 2
#define LEFT 3
#define RIGHT 4
#define MAX 6


/*

   * Code to generate spiral matrix for n elements where n >= 1

   * To generate spiral matrix for n elements just
   * change the value of MAX to whatever u want :)

   * Author : Raza ([email protected])

*/


void main()
{

	int initial_direction = UP , n = MAX , p = 1 ;    /* intial_direction

	is set to UP because we need to start moving right */

	int r ,c , a[MAX][MAX];

	int row_right  = 0 , column_down = n-1 , row_left = n-1 , column_up = 0 ;

	clrscr ();

	//Set all elements of the matrix to 0

	for(r = 0 ; r < MAX ; r++)
	{
		for(c = 0 ; c < MAX ; c++)
			a[r][c] = 0 ;

	}


	//Generate elements of the spiral matrix

	while(p != n*n+1)
	{

	      if(initial_direction == UP)
	      {
			//Move RIGHT

			r = row_right++ ;

			for(c = 0 ; c < n ; c++)
			{
				if(a[r][c] == 0)
					a[r][c] = p++;

			}




			initial_direction = RIGHT ;
	      }
	      else if(initial_direction == RIGHT)
	      {
			//Move down

			c = column_down-- ;

			for(r = 0 ; r < n ; r++)
			{

				if(a[r][c] == 0)
					a[r][c] = p++;
			}


			initial_direction = DOWN ;




	      }
	      else if(initial_direction == DOWN)
	      {
			//Move left

			r = row_left-- ;

			for(c = n-1 ; c >= 0 ; c--)
			{
				if(a[r][c] == 0)
					a[r][c] = p++;

			}

			initial_direction = LEFT ;





	      }
	      else if(initial_direction == LEFT)
	      {
			//Move up

			c = column_up++;

			for(r = n-1 ; r >= 0 ; r--)
			{

				if(a[r][c] == 0)
				  a[r][c] = p++;

			}


			initial_direction = UP ;
	      }

	}


	//Print the matrix

	printf("\n\n");

	for(r = 0 ; r < MAX ; r++)
	{
	      for(c = 0 ; c < MAX ; c++)
		  printf("%4d ",a[r][c]);

	      printf("\n");



	}

}
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