Operations on Queue !

#include<stdio.h>
#include<conio.h>
#define max 10
void insert(int);
int deletee();
void display();
int f=-1;
int r=-1;
int a[max];
void main()
{
    int ch,value;
    while(1)
    {
    printf("\n1.Insert Data");
    printf("\n2.Delete Data");
    printf("\n3.Display Data");
    printf("\n4.Exit");
    printf("\nEnter Choice\n");
    scanf("%d",&ch);
    switch(ch)
    {
    case 1:
        if(r==9)
        {
            printf("\nQueue Overflow");
        }
        else{
            printf("\nEnter Value to Insert\n");
            scanf("%d",&value);
            insert(value);
        }
        break;
    case 2:
        if(f==-1)
        {
            printf("\nQueue Underflow");
        }
        else{
        int n=deletee();
        f++;
        printf("value %d deleted",n);
        }
        break;
    case 3:
        display();
        break;
    case 4:
        exit(1);
        break;
    default:
        printf("\Invalid Input");
        break;
    }
    }
}
void insert(int value)
{
    if(f==-1 && r==-1)
    {
        f++;
        r++;
        a[r]=value;
    }
    else{
        r++;
        a[r]=value;
    }
}

int deletee()
{
    return a[f];
}
void display()
{
    int i;
    printf("\n The list of Data are:\n");
    for(i=f;i<=r;i++)
    {
        printf("\n%d",a[i]);
    }
}