use TryParse, if you will enter int then it will convert as it is, but if you will enter string in zip code it will give you 0.
static void Main(string[] args)
{
string firstname;
string lastname;
string birthdate;
string addressline1;
string adressline2;
string city;
string stateorprovince;
int ziporpostalcode;
string country;
Console.WriteLine("enter your first name");
firstname = Console.ReadLine();
Console.WriteLine("enter last name");
lastname = Console.ReadLine();
Console.WriteLine("brithdate");
birthdate = Console.ReadLine();
Console.WriteLine("address line 1");
addressline1 = Console.ReadLine();
Console.WriteLine("addres line 2");
adressline2 = Console.ReadLine();
Console.WriteLine("city");
city = Console.ReadLine();
Console.WriteLine("state/province");
stateorprovince = Console.ReadLine();
Console.WriteLine("zip or postal code");
Int32.TryParse(Console.ReadLine(), out ziporpostalcode);
Console.WriteLine("country");
country = Console.ReadLine();
}