Priority Queue in Data Structure

Example: Program for Priority Queue

#include <stdio.h>
#include <stdlib.h>
#define MAX 5

void insert_by_priority(int);
void delete_by_priority(int);
void create();
void check(int);
void display_pqueue();

int pri_que[MAX];
int front, rear;

void main()
{
    int n, ch;  
    printf("\n1 Insert");
    printf("\n2 Delete");
    printf("\n3 Display");
    printf("\n4 Exit");  
    create();  
    while (1)
    {
        printf("\nEnter your choice : ");    
        scanf("%d", &ch);   
        switch (ch)
        {
        case 1:
            printf("\nInsert Element : ");
            scanf("%d",&n);
            insert_by_priority(n);
            break;
        case 2:
            printf("\nEnter Element to Delete : ");
            scanf("%d",&n);
            delete_by_priority(n);
            break;
        case 3:
            display_pqueue();
            break;
        case 4:
            exit(0);
        default:
            printf("\n Invalid Choice");
        }
    }
}  
void create() //Create Function
{
    front = rear = -1;
}  
void insert_by_priority(int data) //Insert Function
{
    if (rear >= MAX - 1)
    {
        printf("\nQueue is Overflow");
        return;
    }
    if ((front == -1) && (rear == -1))
    {
        front++;
        rear++;
        pri_que[rear] = data;
        return;
    }    
    else
        check(data);
    rear++;
}  
void check(int data) //Check Function - to check priority and place element
{
    int i,j;  
    for (i = 0; i <= rear; i++)
    {
        if (data >= pri_que[i])
        {
            for (j = rear + 1; j > i; j--)
            {
                pri_que[j] = pri_que[j - 1];
            }
            pri_que[i] = data;
            return;
        }
    }
    pri_que[i] = data;
}  
void delete_by_priority(int data) //Delete Function
{
    int i;  
    if ((front==-1) && (rear==-1))
    {
        printf("\nQueue is empty no elements to delete");
        return;
    }  
    for (i = 0; i <= rear; i++)
    {
        if (data == pri_que[i])
        {
            for (; i < rear; i++)
            {
                pri_que[i] = pri_que[i + 1];
            }
            pri_que[i] = -99;
            rear--;
            if (rear == -1)
               front = -1;
            return;
        }
    }
    printf("\n%d not found in queue to delete", data);
}
void display_pqueue() //Display Function
{
    if ((front == -1) && (rear == -1))
    {
        printf("\nQueue is empty");
        return;
    }  
    for (; front <= rear; front++)
    {
        printf(" %d ", pri_que[front]);
    }
     front = 0;
}