Implement BFS( Bredth First Search) in c || With Simple code

  // write a program in c to implement BFS (Bredth First Search)
  #include <stdio.h>
  int a[20][20], q[20], visited[20], n, i, j, f = 0, r = -1;

  void bfs(int v)
  {
	for (i = 1; i <= n; i++)
		if (a[v][i] && !visited[i])
			q[++r] = i;
	if (f <= r)
	{
		visited[q[f]] = 1;
		bfs(q[f++]);
	}
  }

  void main()
  {
	int v;
	printf("\n Enter the number of vertices: \n");
	scanf("%d", &n);

	for (i = 1; i <= n; i++)
	{
		q[i] = 0;
		visited[i] = 0;
	}

	printf("\n Enter graph data in matrix form:\n");
	for (i = 1; i <= n; i++)
	{
		for (j = 1; j <= n; j++)
		{
			scanf("%d", &a[i][j]);
		}
	}

	printf("\n Enter the starting vertex:");
	scanf("%d", &v);
	bfs(v);
	printf("\n The node which are reachable are:\n");

	for (i = 1; i <= n; i++)
	{
		if (visited[i])
			printf("%d\t", i);
		else
		{
			printf("\n Bfs is not possible. Not all nodes are reachable");
			break;
		}
	}
  }

When the above program is executed, it produces following results --<\b>
OUTPUT NO :-

    Enter the number of vertices:
    4
    Enter graph data in matrix form:
   1 1 1 1
   0 1 0 0
   0 0 1 0
   0 0 0 1

    Enter the starting vertex:1
   
    The node which are reachable are:
   1       2       3       4

OUTPUT NO :- 02

    Enter the number of vertices: 
   4

       Enter graph data in matrix form:
   1 1 1 1
   0 1 0 0
   0 0 1 0
   0 0 0 1
   
    Enter the starting vertex:2
   
    The node which are reachable are:
   
    Bfs is not possible. Not all nodes are reachable