Queue implementation on linked lists in C language

Queue implementation on linked lists in C language

/*
This is a program showing the queue implimentation on linked list
program writtem by RP Singh
compiled and tested on C-free4.0 standard
*/
#include
#include
#include
struct node1
{
    int item;
    struct node1 *next;
};
typedef struct node1 node;        //defining datatype node

struct q1
{
    node *front;
    node *rear;
    int length;
};
typedef struct q1 queue;        //defining queue datatype

void enqueue(node *, queue *);
node *dequeue(queue *);
int queue_length(queue *);
void view_queue(queue *);
node *create_node(void);
void fill_node(node *);


int main()
{
    int i,j;
    node *current_node;
    queue que;                    //local queue
    que.front=NULL;
    que.rear=NULL;
    que.length=0;
    printf("This is a demo program to show working of queues");
    anchor:                    //anchor is a label
    printf("\n\nyou have following options\n");
    printf("1. enqueue an item\n2. dequeue an item\n3. view queue\n");
    printf("4. count items in queue\n5. exit program\n\n");
    scanf("%d",&j);
    switch(j)
    {
        case 1:
            printf("\nEnter a number to be enqueued =>\t");
            current_node=create_node();
            fill_node(current_node);
            enqueue(current_node, &que);
            goto anchor;
        case 2:
            current_node = dequeue(&que);
            if(current_node)
            printf("The item %d dequeued successfully\n",current_node->item);
            goto anchor;
        case 3:
            view_queue(&que);
            goto anchor;
        case 4:
            printf("total items in the queue are %d\n",que.length);
            goto anchor;
        case 5:
            printf("Thank you\n");
            exit(0);
            goto anchor;
        default:
            printf("Invalid choice...!!!\n try choosing again\n\n");
            goto anchor;
    }
  
    return 0;
}

void enqueue(node *p,queue *q)                    //definition of enqueue function
{
    if(q->rear==NULL&&q->front==NULL)
    {
        q->rear=p;
        q->front=p;
    }
    else
    {
        q->rear->next=p;
        q->rear=p;
    }
    q->length++;
    printf("item %d enqueued successfully.\n",p->item);
}

node *dequeue(queue *q)                    //definition of dequeue function
{
    node *temp=NULL;
    if(q->rear==NULL&&q->front==NULL)        //this is the case when queue is empty
    {
        printf("queue is empty hence can not be dequeued\n");
        return temp;
    }
    else if(q->rear==q->front&&q->front!=NULL)    //this is the case when queue has only one node
    {
        temp=q->front;
        q->front=NULL;
        q->rear=NULL;
    }
    else
    {
        temp=q->front;
        q->front=q->front->next;
    }
    q->length--;
    return temp;
}

void view_queue(queue *q)
{
    node *temp_front;
    temp_front=q->front;
    if(q->length==0)
    {
        printf("\nThe queue is empty...!!!\n");
        return;
    }
    printf("The queue is\n");
    while(temp_front!=NULL)
    {
        printf("%d -> ",temp_front->item);
        temp_front=temp_front->next;
    }
    printf("\n");
    return;
}

node *create_node()                    //function to create a blank node
{
    node *temp;
    temp=(node*)malloc(sizeof(node));
    temp->next=NULL;
    return temp;
}

void fill_node(node *p)                    //function to fill a blank node with values taken from user
{
    int i;
    scanf("%d",&i);                    //this is the value taken from user
    p->item=i;
}

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