Queue using linked list

/*
Write a program for queue using linked list

*/

#include<stdio.h>
#include<stdlib.h>

struct node
{

int info;

struct node *link;

}*front=NULL,*rear=NULL;

void insert(int item);

int del();

int peek();

int isEmpty();

void display();

main()
{

int choice,item;

while(1)

{

printf("1.Insert\n");

printf("2.Delete\n");

printf("3.Display the element at the front\n");

printf("4.Display all elements of the queue\n");

printf("5.Quit\n");

printf("Enter your choice : ");

scanf("%d", &choice);

switch(choice)

{

case 1:

printf("Input the element for adding in queue : ");

scanf("%d",&item);

insert(item);

break;

case 2:

printf("Deleted element is %d\n",del());

break;

case 3:

printf("Element at the front of the queue is %d\n", peek() );

break;

case 4:

display();

break;

case 5:

exit(1);

default :

printf("Wrong choice\n");

}
}
}

void insert(int item)

{

struct node *tmp;

tmp=(struct node *)malloc(sizeof(struct node));

if(tmp==NULL)

{

printf("Memory not available\n");

return;

}

tmp->info = item;

tmp->link=NULL;

if(front==NULL) /*If Queue is empty*/

front=tmp;

else

rear->link=tmp;

rear=tmp;

}

int del()

{

struct node *tmp;

int item;

if( isEmpty( ) )

{

printf("Queue Underflow\n");

exit(1);

}

tmp=front;

item=tmp->info;

front=front->link;

free(tmp);

return item;

}

int peek()

{

if( isEmpty( ) )

{

printf("Queue Underflow\n");

exit(1);

}

return front->info;

}

int isEmpty()

{

if(front==NULL)

return 1;

else

return 0;

}

void display()

{

struct node *ptr;

ptr=front;

if(isEmpty())

{

printf("Queue is empty\n");

return;

}

printf("Queue elements :\n\n");

while(ptr!=NULL)

{

printf("%d ",ptr->info);

ptr=ptr->link;

}

printf("\n\n");

}