void delete_()
{
    int i,n;
    for(i=0; i<counter; i++)
        printf("%d)first name: %s\nlast name: %s\nAddress: %s\nCity: %s\nNumber: %s\n",i+1,person[i].fname,person[i].lname,person[i].address,person[i].city,person[i].number);
    printf("enter the number of contact you want to delete: ");
    scanf("%d",&n);
    n--;
    for(i=n; i<=counter; i++)
    {
        strcpy(person[i].fname,person[i+1].fname);
        strcpy(person[i].lname,person[i+1].lname);
        strcpy(person[i].address,person[i+1].address);
        strcpy(person[i].city,person[i+1].city);
        strcpy(person[i].number,person[i+1].number);
    }
    counter--;
    system("cls");
    printf("\nA contact has been deleted.");
}