我真的必须给我所有的变量一个初始值吗

可能重复：
当默认值为0时，为什么我必须在C#中为int赋值？

我刚开始通过编写一个名为Journal的人工应用程序来学习C#。在解析日志文件的函数中，我声明了变量DateTime currentEntryDate。在我到达定义新条目的行之前，它不会得到值。当我到达条目行的第二次时，该变量将用于为上一个条目创建JournalEntry类的实例。

问题是，使用变量的代码无法编译：

使用未分配的本地变量"currentEntryDate">

这对我来说毫无意义。为了让编译器满意，我真的必须给变量一个浪费的初始值吗？我肯定误解了什么，或者我的代码中有错误。

Pastebin上的代码：Journal.cs。我已经突出显示了相关的行。

代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.IO;
namespace Journal
{
    class Journal
    {
        public List<JournalEntry> Entries;
        private static readonly string EntryLineRegex =
            @"-- Entry: (?<title>.*) '((?<year>'d{4})-(?<month>'d{2})" +
            @"-(?<day>'d{2})')";
        public static Journal FromFile(string filePath)
        {
            Journal returnValue = new Journal();
            StreamReader fileReader = new StreamReader(filePath);
            // Prepare variables for parsing the journal file.
            bool hitFirstEntry = false;
            DateTime currentEntryDate;
            string currentEntryTitle;
            StringBuilder currentEntryText = new StringBuilder();
            // Prepare a regular expression for the entry lines.
            Regex entryLineRegex = new Regex(EntryLineRegex);
            while (!fileReader.EndOfStream)
            {
                string line = fileReader.ReadLine();
                if (line.StartsWith("--"))
                {
                    // Is this the first entry encountered? If so, don't try to
                    // process the previous entry.
                    if (!hitFirstEntry)
                    {
                        hitFirstEntry = true;
                    }
                    else
                    {
                        // Create a JournalEntry with the current entry, then
                        // reset for the next entry.
                        returnValue.Entries.Add(
                            new JournalEntry(
                                currentEntryText.ToString(), currentEntryDate
                            )
                        );
                        currentEntryDate = new DateTime();
                        currentEntryText.Clear();
                    }
                    // Extract the new entry title and date from this line and
                    // save them.
                    Match entryMatch = entryLineRegex.Match(line);
                    GroupCollection matches = entryMatch.Groups;
                    currentEntryDate = new DateTime(
                        Convert.ToInt16(matches["year"].Value),
                        Convert.ToInt16(matches["month"].Value),
                        Convert.ToInt16(matches["day"].Value)
                    );
                    currentEntryTitle = matches["title"].Value;
                }
                else
                {
                    currentEntryText.Append(line);
                }
            }
            return returnValue;
        }
    }
    class JournalEntry
    {
        public string Text;
        public DateTime EntryDate;
        public JournalEntry(string text, DateTime entryDate)
        {
            this.Text = text;
            this.EntryDate = entryDate;
        }
    }
}

string line = fileReader.ReadLine();
while (line != null)
{
    // Extract the new entry title and date from this line and
    // save them.
    Match entryMatch = entryLineRegex.Match(line);
    GroupCollection matches = entryMatch.Groups;
    currentEntryDate = new DateTime(
        Convert.ToInt16(matches["year"].Value),
        Convert.ToInt16(matches["month"].Value),
        Convert.ToInt16(matches["day"].Value)
    );
    currentEntryTitle = matches["title"].Value;
    while ((line = fileReader.ReadLine()) != null && !line.StartsWith("--"))
    {
        currentEntryText.Append(line);
    }
    // Create a JournalEntry with the current entry, then
    // reset for the next entry.
    returnValue.Entries.Add(
        new JournalEntry(
            currentEntryText.ToString(), currentEntryDate
        )
    );
    currentEntryText.Clear();
}

        bool isFirstTime = true;
        DateTime localVarToBeAssigned;
        while (true)
        {
            if (isFirstTime)
            {
                isFirstTime = false;
            }
            else
            {
                // this reads the variable
                Console.WriteLine(localVarToBeAssigned);
            }
            // this assigns the variable
            localVarToBeAssigned = DateTime.Now;
        }

DateTime? currentEntryDate = null