Circular Queue

#include<stdio.h>

#define MAX 4

typedef struct
{
    int q[ MAX ], f, r, flag;
}queue_t;

int isEmpty ( queue_t *t )
{
    return ( !t->flag );
}

void insert ( queue_t *t, int ele )
{
    if ( t->f == ( t->r + 1 ) % MAX && t->flag == 1 )
    {
        printf ( "Queue Overflow\n" );
        return;
    }
    else
    {
        t->r = ( t->r + 1 ) % MAX;
        t->q[ t->r ] = ele;
        t->flag = 1;
    }
}

int del( queue_t *t )
{
    int z;
    if ( isEmpty ( t ) )
    {
        printf ( "Queue Underflow\n" );
        return -1;
    }
    else
    {
        z = t->q[ t->f ];
        t->f = ( t->f + 1 ) % MAX;
        if ( t->f == ( t->r + 1 ) % MAX )
            t->flag = 0;
        return z;
    }
}

void display ( queue_t *t )
{
    int i;
    if ( isEmpty ( t ) )
    {
        printf ( "Queue Empty\n" );
        return;
    }
    i = t->f;
    while ( 1 )
    {
        printf ( "%d\t", t->q[ i ] );
        if ( i == t->r )
            break;
        i = ( i + 1 ) % MAX;
    }
}

int queueFront ( queue_t *t )
{
    return t->q[ t->f ];
}

void main ( )
{
    int choice, ele;
    queue_t queue = { .r = -1, .f = 0, .flag = 0 };
    while ( 1 )
    {
        printf ( "1:\tInsert\n2:\tDelete\n3:\tQueue Front\n4:\tDisplay\n0:\tEXIT\nCHOICE:\t" );
        scanf ( "%d", &choice );
        if ( !choice )
            break;
        switch ( choice )
        {
            case 1:
                printf ( "Enter element to insert:\t" );
                scanf ( "%d", &ele );
                insert ( &queue, ele );
                display ( &queue );
                break;
            case 2:
                if ( isEmpty ( &queue ) )
                {
                    printf ( "Queue Underflow.\n" );
                    continue;
                }
                printf ( "Deleted element:\t%d\n", del ( &queue ) );
                display ( &queue );
                break;
            case 3:
                if ( isEmpty ( &queue ) )
                {
                    printf ( "Queue Empty.\n" );
                    continue;
                }
                printf ( "Queue Front:\t%d\n", queueFront ( &queue ) );
                break;
            case 4:
                display ( &queue );
                break;
            default:
                printf ( "Invalid Input.\nTry Again.\n" );
                continue;
        }
        printf ( "\n" );
    }
    display ( &queue );
}