How to implement the priority queue using heaps in C?

Question

An element with high priority is appears before low priority element, can someone help me to write the Priority Queue Implementation?

Thanks in advance?

Answer 1

//Priority Queue with heap:


#include<stdio.h>
#include<malloc.h>
void insert();
void del();
void display();

struct node
{
int priority;
int info;
struct node *next;
}*start=NULL,*q,*temp,*new;


typedef struct node N;
int main()
{
int ch;
clrscr();
do
{
printf("\n[1] INSERTION\t[2] DELETION\t[3] DISPLAY [4] EXIT\t:");
scanf("%d",&ch);
switch(ch)
{
case 1:insert();
break;
case 2:del();
break;
case 3:display();
break;
case 4:
break;
}
}
while(ch<4);
}

void insert()
{
int item,itprio;
new=(N*)malloc(sizeof(N));
printf("ENTER THE ELT.TO BE INSERTED :\t");
scanf("%d",&item);
printf("ENTER ITS PRIORITY :\t");
scanf("%d",&itprio);
new->info=item;
new->priority=itprio;
new->next=NULL;
if(start==NULL )
{
//new->next=start;
start=new;
}
else if(start!=NULL&&itprio<=start->priority)
{  new->next=start;
start=new;
}
else
{
q=start;
while(q->next != NULL && q->next->priority<=itprio)
{q=q->next;}
new->next=q->next;
q->next=new;
}
}

void del()
{
if(start==NULL)
{
printf("\nQUEUE UNDERFLOW\n");

}
else
{
new=start;
printf("\nDELETED ITEM IS %d\n",new->info);
start=start->next;
//free(start);
}
}

void display()
{
temp=start;
if(start==NULL)
printf("QUEUE IS EMPTY\n");
else
{
printf("QUEUE IS:\n");
if(temp!=NULL)
for(temp=start;temp!=NULL;temp=temp->next)
{
printf("\n%d priority =%d\n",temp->info,temp->priority);
//temp=temp->next;
}
}
}