Linear Queue

#include <stdio.h>
#include <conio.h>
#define MAX 10 // Changing this value will change length of array
int queue[MAX];
int front = -1, rear = -1;
void insert(void);
int delete_element(void);
int peek(void);
void display(void);

int main()
{
      int option, val;
      do
      {
            printf("\n\n ***** MAIN MENU *****");
            printf("\n 1. Insert an element");
            printf("\n 2. Delete an element");
            printf("\n 3. Peek");
            printf("\n 4. Display the queue");
            printf("\n 5. EXIT");
            printf("\n Enter your option : ");
            scanf("%d", &option);
            switch(option)
             {
                  case 1: insert();
                          break;
                  case 2: val = delete_element();
                          if (val != -1)
                          printf("\n The number deleted is : %d", val);
                          break;
                  case 3: val = peek();
                          if (val != -1)
                          printf("\n The first value in queue is : %d", val);
                          break;
                  case 4: display();
                          break;
             }
         }while(option != 5);
      getch();
      return 0;
}
void insert()
{
      int num;
      printf("\n Enter the number to be inserted in the queue : ");
      scanf("%d", &num);
      if(rear == MAX-1)
      printf("\n OVERFLOW");
      else if(front == -1 && rear == -1)
      front = rear = 0;
      else
      rear++;
      queue[rear] = num;
}
int delete_element()
{
      int val;
      if(front == -1 || front>rear)
      {
            printf("\n UNDERFLOW");
            return -1;
      }
      else
      {
            val = queue[front];
            front++;
            if(front > rear)
            front = rear = -1;
            return val;
      }
}
int peek()
{
      if(front==-1 || front>rear)
      {
            printf("\n QUEUE IS EMPTY");
            return -1;
      }
      else
      {
            return queue[front];
      }
}
void display()
{
      int i;
      printf("\n");
      if(front == -1 || front > rear)
            printf("\n QUEUE IS EMPTY");
      else
      {
            for(i = front;i <= rear;i++)
            printf("\t %d", queue[i]);
      }
}