Queues using linked list added

Author: akshit04

Queues_using_linked_list/Queues_using_linked_list.c

@@ -0,0 +1,172 @@
+/*
+ * C Program to Implement Queue Data Structure using Linked List
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <malloc.h>
+
+struct node
+{
+    int info;
+    struct node *ptr;
+}*front,*rear,*temp,*front1;
+
+int frontelement();
+void enq(int data);
+void deq();
+void empty();
+void display();
+void create();
+void queuesize();
+
+int count = 0;
+
+void main()
+{
+    int no, ch, e;
+
+    printf("\n 1 - Enque");
+    printf("\n 2 - Deque");
+    printf("\n 3 - Front element");
+    printf("\n 4 - Empty");
+    printf("\n 5 - Exit");
+    printf("\n 6 - Display");
+    printf("\n 7 - Queue size");
+    create();
+    while (1)
+    {
+        printf("\n Enter choice : ");
+        scanf("%d", &ch);
+        switch (ch)
+        {
+            case 1:
+            printf("Enter data : ");
+            scanf("%d", &no);
+            enq(no);
+            break;
+            case 2:
+            deq();
+            break;
+            case 3:
+            e = frontelement();
+            if (e != 0)
+                printf("Front element : %d", e);
+            else
+                printf("\n No front element in Queue as queue is empty");
+            break;
+            case 4:
+            empty();
+            break;
+            case 5:
+            exit(0);
+            case 6:
+            display();
+            break;
+            case 7:
+            queuesize();
+            break;
+            default:
+            printf("Wrong choice, Please enter correct choice  ");
+            break;
+        }
+    }
+}
+
+/* Create an empty queue */
+void create()
+{
+    front = rear = NULL;
+}
+
+/* Returns queue size */
+void queuesize()
+{
+    printf("\n Queue size : %d", count);
+}
+
+/* Enqueing the queue */
+void enq(int data)
+{
+    if (rear == NULL)
+    {
+        rear = (struct node *)malloc(1*sizeof(struct node));
+        rear->ptr = NULL;
+        rear->info = data;
+        front = rear;
+    }
+    else
+    {
+        temp=(struct node *)malloc(1*sizeof(struct node));
+        rear->ptr = temp;
+        temp->info = data;
+        temp->ptr = NULL;
+
+        rear = temp;
+    }
+    count++;
+}
+
+/* Displaying the queue elements */
+void display()
+{
+    front1 = front;
+
+    if ((front1 == NULL) && (rear == NULL))
+    {
+        printf("Queue is empty");
+        return;
+    }
+    while (front1 != rear)
+    {
+        printf("%d ", front1->info);
+        front1 = front1->ptr;
+    }
+    if (front1 == rear)
+        printf("%d", front1->info);
+}
+
+/* Dequeing the queue */
+void deq()
+{
+    front1 = front;
+
+    if (front1 == NULL)
+    {
+        printf("\n Error: Trying to display elements from empty queue");
+        return;
+    }
+    else
+        if (front1->ptr != NULL)
+        {
+            front1 = front1->ptr;
+            printf("\n Dequed value : %d", front->info);
+            free(front);
+            front = front1;
+        }
+        else
+        {
+            printf("\n Dequed value : %d", front->info);
+            free(front);
+            front = NULL;
+            rear = NULL;
+        }
+        count--;
+    }
+
+/* Returns the front element of queue */
+    int frontelement()
+    {
+        if ((front != NULL) && (rear != NULL))
+            return(front->info);
+        else
+            return 0;
+    }
+
+/* Display if queue is empty or not */
+    void empty()
+    {
+       if ((front == NULL) && (rear == NULL))
+        printf("\n Queue empty");
+    else
+     printf("Queue not empty");
+}