Perform an iterative BFS traversal over a graph represented using an adjacency list.

#include<stdio.h>
#include<stdlib.h>
#define N 20

typedef int element;

typedef struct 
{
	element data[N]; /* queue content */
	int front, length;
} queue;


typedef struct node {
	int vertexNumber;
	struct node * next;
} node;
typedef struct {
	int V;
	int E;
	node** Adj;  //array of linked list
} Graph;




queue CreateQueue()
{
	queue q;
	q.front = 0; q.length=0;
	return q;
}
int isEmptyQueue(queue q)
{
	return q.length == 0;
}

int isFullQueue(queue q)
{
	return q.length ==N;
}

int EnQueue(queue *q, element e)
{
	if (isFullQueue(*q)) return 0;
	q->data[(q->front + q->length)%N] = e;
	q->length = q->length + 1;
	return 1;
}

int DeQueue(queue *q)
{
	if (isEmptyQueue(*q)) return 0;
	q->front=(q->front + 1) % N;
	q->length--;
	return 1;
}

int Front(queue q, element *e)
{
	if (isEmptyQueue(q)) return 0;
	*e = q.data[q.front];
	return 1;
}

 




Graph* adjacencyList() {
	int i, x, y;
	node * temp, *temp2;
	Graph* G=(Graph*) malloc(sizeof(Graph));

	printf("Enter the number of Vertices: ");
	scanf("%d", &G->V);
	printf("Enter the number of Edges: ");
	scanf("%d", &G->E);
	G->Adj = (node **)malloc(G->V * sizeof(node));
	for (i = 0; i < G->V; i++) {
		G->Adj[i] = (node *)malloc(G->V * sizeof(node));
		G->Adj[i]->vertexNumber = i;
		G->Adj[i]->next = NULL;
	}
 
	for (i = 0; i < G->E; i++) {
		printf("Enter the edge: ");
		scanf("%d %d", &x,&y);
		temp = (node*)malloc(sizeof(node));
		temp->vertexNumber = y;
        	temp->next = NULL;
        
		temp2 = G->Adj[x];
		while (temp2->next != NULL)
			temp2 = temp2->next;
		temp2->next = temp;
		
	}
	return G;
}

void BFSTraversal(Graph *G, int index, int Visited[]) {
	queue q;
	element e;
    	node * head;
   
	q=CreateQueue();
 
	EnQueue(&q,index);
	Visited[index] = 1;

	while(Front(q,&e))
	{
	    DeQueue(&q);
	    printf("%d ",e);
	    head=G->Adj[e]->next;
	    while(head)
	    {
	        if(!Visited[head->vertexNumber])
	        {
	            Visited[head->vertexNumber] = 1;
	            EnQueue(&q,head->vertexNumber);
	        }
	        head = head->next;
	    }
	}
}

void BFS(Graph *G) {
	int i;
	int *Visited;

	Visited = (int *)malloc(G->V * sizeof(int));
	for (i = 0; i < G->V; i++)
		Visited[i] = 0;

	// this loop is required if the grpah has more than one component
	for (i = 0; i < G->V; i++)
		if (!Visited[i])
			BFSTraversal(G, i, Visited);
}



void test() {
	Graph *G = adjacencyList();
	BFS(G);
}

int main()
{
	test();
	return 0;
}