C program to implement a priority queue

#include <stdio.h>
#include <malloc.h>
#include <conio.h>
struct node
{
int data;
int priority;
struct node *next;
}
struct node *start=NULL;
struct node *insert(struct node *);
struct node *delete(struct node *);
void display(struct node *);
int main()
{
int option;
clrscr();
do
{
 printf("\n *****MAIN MENU*****);
 printf("\n 1. INSERT");
 printf("\n 2. DELETE");
 printf("\n 3. DISPLAY");
 printf("\n 4. EXIT");
 printf("\n Enter your option : ");
 scanf( "%d", &option);
switch(option)
 {
 case 1:
 start=insert(start);
break;
 case 2:
 start = delete(start);
break;
 case 3:
 display(start);
break;
 }
}while(option!=4);
}
struct node *insert(struct node *start)
{
int val, pri;
struct node *ptr, *p;
ptr = (struct node *)malloc(sizeof(struct node));
printf("\n Enter the value and its priority : " );
scanf( "%d %d", &val, &pri);
ptr–>data = val;
ptr–>priority = pri;
if(start==NULL || pri < start–>priority )
{
 ptr–>next = start;
 start = ptr;
}
else
{
 p = start;
while(p–>next != NULL && p–>next–>priority <= pri)
 p = p–>next;
 ptr–>next = p–>next;
 p–>next = ptr;
}
return start;
}
struct node *delete(struct node *start)
{
struct node *ptr;
if(start == NULL)
{
 printf("\n UNDERFLOW" );
 return;
}
else

{
 ptr = start;
 printf("\n Deleted item is: %d", ptr–>data);
 start = start–>next;
 free(ptr);
}
return start;
}
void display(struct node *start)
{
struct node *ptr;
ptr = start;
if(start == NULL)
 printf("\nQUEUE IS EMPTY" );
else
{
 printf("\n PRIORITY QUEUE IS : " );
while(ptr != NULL)
 {
 printf( "\t%d[priority=%d]", ptr–>data, ptr–>priority );
 ptr=ptr–>next;
 }
}
}

*****MAIN MENU*****
1. INSERT
2. DELETE
3. DISPLAY
4. EXIT
Enter your option : 1
Enter the value and its priority : 5 2
Enter the value and its priority : 10 1
Enter your option : 3
PRIORITY QUEUE IS :
10[priority = 1] 5[priority = 2]
Enter your option : 4