return types

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using arun.CSharp.Namespaces;

public class Friend

        {
        public static void Main(string[] args)
        //public static void Main()

        {

        Friend[] friend = new Friend[4];
        int x;
        string firstname;
        string surname;
        string phonenumber;
        int month;
        int day;


        for (x = 0; x < friend.Length; ++x)
        {
            GetData(out firstname, out surname, out phonenumber, out month, out day);
            friend[x] = new Friend(firstname, surname, phonenumber, month, day);
        }

        Array.Sort(friend);
        Console.WriteLine("Sorted List:");
        for (x = 0; x < friend.Length; ++x)
        Display(friend[x]);

        Console.ReadLine();
        }

        public static void GetData(out string firstname, out string surname, out string phonenumber, out int month, out int day)
        {
        string inString;
        Console.Write("Please enter your friend's firstname: ");
        inString = Console.ReadLine();
        firstname = Convert.ToString(inString);
        Console.Write("Please enter your friend's surname: ");
        inString = Console.ReadLine();
        surname = Convert.ToString(inString);
        Console.Write("Please enter your friend's number: ");
        inString = Console.ReadLine();
        phone = Convert.ToString(inString);
        Console.Write("Please enter your friend's birth MONTH: ");
        inString = Console.ReadLine();
        month = Convert.ToInt32(inString);
        Console.Write("Please enter your friend's birth DAY: ");
        inString = Console.ReadLine();
        day = Convert.ToInt32(inString);
        }

        public static void Display(Friend fri)
        {
        Console.WriteLine("0,5}{1,-10}{2,6}{3,6}{4,6}",
        fri.Name, fir.surname, fri.Phone, fri.Month, fri.Day);
        }
        }

        public class Fri: IComparable
        {
        private string firstname;
        private string surname;
        private string phone;
        private int month;
        private int day;

        public string Firstname { get; set; }
        public string Surname { get; set; }
        public string Phone { get; set; }
        public int Month { get; set; }
        public int Day { get; set; }

        public Friend(string friendFirstName, string friendSurName, string friendNumber, int friendMonth, int friendDay)
        {

        firstName = friendFirstName;
        surname = friendSurName;
        Phone = friendNumber;
        Month = friendMonth;
        Day = friendDay;
        }

        int IComparable.CompareTo(object o)
        {
        int returnVal;
        Friend temp = (Friend)o;
        if (this.Name > temp.Name)
        returnVal = 1;
        else
        if (this.Name < temp.Name)
        returnVal = -1;
        else
        returnVal = 0;
        return returnVal;
        }
        }




I am currently working on this code but i dont understand why it is asking me for a return type can anyone explain this to me I would be great thanks gemma