Create queue_linked_list.c

Implementation of Queue using Linked List.

data_structures/linked_list/queue_linked_list.c

@@ -0,0 +1,149 @@
+/* Queue using Linked List - Program to create a queue ADT using linked list. ADT should support the following operations
+1)  Createqueue
+2)  Insert into the queue
+3)  Delete from the queue
+4)  destroyqueue
+*/
+
+/* queue q declared globally */
+
+#include <stdio.h>
+#include <stdlib.h>
+#define NULL 0	
+
+struct  node
+{
+  int  data ;
+  struct  node  *next ;
+} ;
+
+struct  queue
+{
+ struct  node  *front , *rear ;
+} ;
+
+struct  queue  q ;
+
+/* This function initializes the queue to empty by making both front and rear as NULL */
+void createqueue()
+{
+  q.front=q.rear=NULL ;
+}
+
+int  empty()
+{
+  if(q.front==NULL)
+    return  1 ;
+  else
+    return  0 ;
+}
+
+void  insert(int  x)
+{
+  struct  node  *pnode ;
+
+  pnode=(struct node*)malloc(sizeof(struct node)) ;
+  if(pnode==NULL)
+  {
+    printf("Memory overflow. Unable to insert.\n") ;
+    exit(1) ;
+  }
+
+  pnode->data=x ;
+  pnode->next=NULL ;   /* New node is always last node */
+
+  if(empty())
+      q.front=q.rear=pnode ;
+  else
+  {
+      (q.rear)->next=pnode ;
+      q.rear=pnode ;
+  }
+}
+
+int  removes()
+{
+  int  x ;
+  struct  node  *p ;
+
+  if(empty())
+  {
+    printf("Queue Underflow. Unable to remove.\n") ;
+    exit(1) ;
+  }
+
+  p=q.front ;
+  x=(q.front)->data ;
+  q.front=(q.front)->next ;
+  if(q.front==NULL)       /* Queue contained only one node */
+       q.rear=NULL ;
+  free(p) ;
+  return  x ;
+}
+
+void  show()
+{
+  struct  node  *p ;
+
+  if(empty())
+    printf("Queue empty. No data to display \n") ;
+  else
+  {
+    printf("Queue from front to rear is as shown: \n") ;
+
+    p=q.front ;
+    while(p!=NULL)
+    {
+      printf("%d ",p->data) ;
+      p=p->next ;
+    }
+
+    printf("\n") ;
+  }
+}
+
+void  destroyqueue()
+{
+  q.front=q.rear=NULL ;
+}
+
+int main()
+{
+  int  x , ch ;
+
+  createqueue() ;
+
+  do
+  {
+    printf("\n\n  Menu: \n") ;
+    printf("1:Insert \n") ;
+    printf("2:Remove \n") ;
+    printf("3:exit \n") ;
+    printf("Enter your choice: ") ;
+    scanf("%d",&ch) ;
+
+    switch(ch)
+    {
+      case 1:
+      printf("Enter element to be inserted: ") ;
+      scanf("%d",&x) ;
+      insert(x) ;
+      show() ;
+      break ;
+
+      case 2:
+      x=removes() ;
+      printf("Element removed is: %d\n",x) ;
+      show() ;
+      break ;
+
+      case 3:
+      break ;
+    }
+  }
+  while(ch!=3) ;
+
+  destroyqueue() ;
+
+ return 0;
+}