Can someone please help me in correcting this circular queue implementation ?

#define MAX 4
#include <stdio.h>
#include <conio.h>

int Queue[MAX], front, rear;

void enqueue(int elem)
{
    if((front == 0 && rear == MAX - 1) || rear == front - 1)
    {
        printf("\n Queue overflow !");
    }
    
     if(front == -1 && rear == -1)
            front = rear = 0;
            
    else if(rear == (MAX -1) && front != 0)
        rear = 0;
    else
        rear = rear + 1;
            
    Queue[rear] = elem;
  
}

int dequeue()
{
    int t;
    if(front == -1)
    {
        printf("\n Queue underflow !");
    }
    

        t = Queue[front];
    
        if(front == rear)
            front = rear = -1;
            
        else if(front = MAX -1 )
            front = 0;
            
        else
            front = front + 1;
}

int size()
{
    return ((MAX - front + rear) % MAX + 1);
}

int isEmpty()
{
    if(front == -1)
        return 1;
        
    else
        return 0;
}

int frontfn()
{
    int t;
     
    if(front == -1)
    {
        printf("\n Queue is empty. \n ");
    }
    else
    {
        t = Queue[front];
        return t;
    }
 
}

void display()
{
    int i;
    if(isEmpty() == 1)
        printf("\n Queue is empty. \n");
        
    else if(rear < front)
    {
        for(i= front; i <= MAX - 1; i++)
            printf(" %d ", Queue[i]);
            
        for(i=0; i <= rear; i++)
            printf(" %d ", Queue[i]);
            
        printf("\n ");
    }
    else
    {
        for(i=front; i <= rear; i++)
            printf(" %d ", Queue[i]);
            
        printf("\n");
    }
}


int main()
{
    int choice, elem;
    char ch, temp;
    front = rear = -1;
 
     printf("\n1. Insert ");
     printf("\n2. Delete");
     printf("\n3. Last entered element ");
     printf("\n4. No. of elements strored ");
     printf("\n5. Is Queue empty ?");
     printf("\n6. Display");
 
 do
 {
    printf("\n Enter the operation to be carried out.\n ");
    scanf("%d", &choice);

    switch(choice)
    { 
        case 1:
            printf("\n Enter the element to be inserted :\n");
            scanf("%d", &elem);
        
            enqueue(elem);
            display();
            break;
            
        case 2:
             elem = dequeue();
             printf("\n The element deleted is %d \n", elem);
             display();
             break;
             
        case 3:
             elem = frontfn();
             printf("\n Last entered element is %d \n", elem);
             break;
             
        case 4:
             elem = size();
             printf("\n No. of elements strored are %d \n", elem);
             break;
             
        case 5:
             elem = isEmpty();
             if(elem == 1)
             {
             printf("\n Queue is empty. \n");
             }
             else
             {
             printf("\n Queue is not empty. \n");
             }
             break;
             
        case 6:
             display();
             break;
             
        default :
            printf("\n Wrong choice !!");
}

printf("\n Do you want to continue ?");
scanf("%c", &temp);
scanf("%c", &ch);
}
while (ch == 'y' || ch == 'Y');
}