Queue implementation by array insert, delete, peek, display

#include<stdio.h>
#define MAX 10
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 S. 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);
    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]);
    }
}