Priority queue using linked list

/*

Write a program for priority queue using linked list

*/

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

struct node
{

int priority;

int info;

struct node *link;

}*front=NULL;


void insert(int item, int item_priority);

int del();

void display();

int isEmpty();

main()
{

int choice,item,item_priority;

while(1)

{

printf("1.Insert\n");

printf("2.Delete\n");

printf("3.Display\n");

printf("4.Quit\n");

printf("Enter your choice : ");

scanf("%d", &choice);

switch(choice)

{

case 1:

printf("Input the item to be added in the queue : ");

scanf("%d",&item);

printf("Enter its priority : ");

scanf("%d",&item_priority);

insert(item, item_priority);

break;

case 2:

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

break;

case 3:

display();

break;

case 4:

exit(1);

default :

printf("Wrong choice\n");

}
}
}

void insert(int item,int item_priority)
{

struct node *tmp,*p;

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

if(tmp==NULL)

{

printf("Memory not available\n");

return;

}

tmp->info=item;

tmp->priority=item_priority;

/*Queue is empty or item to be added has priority more than first element*/

if( isEmpty() || item_priority < front->priority )

{

tmp->link=front;

front=tmp;

}

else

{

p = front;

while( p->link!=NULL && p->link->priority<=item_priority )

p=p->link;

tmp->link=p->link;

p->link=tmp;

}
}

int del()
{

struct node *tmp;

int item;

if( isEmpty() )

{

printf("Queue Underflow\n");

exit(1);

}

else

{

tmp=front;

item=tmp->info;

front=front->link;

free(tmp);

}

return item;

}

int isEmpty()
{

if( front == NULL )

return 1;

else

return 0;

}

void display()
{

struct node *ptr;

ptr=front;

if( isEmpty() )

printf("Queue is empty\n");

else

{

printf("Queue is :\n");

printf("Priority Item\n");

while(ptr!=NULL)

{

printf("%5d %5d\n",ptr->priority,ptr->info);

ptr=ptr->link;

}
}
}