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PODo I really have to give an initial value to all my variables?
 

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  1. PODo I really have to give an initial value to all my variables?
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    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/1423437/why-do-i-have-to-assign-a-value-to-an-int-in-c-sharp-when-defaults-to-0">Why do I have to assign a value to an int in C# when defaults to 0?</a> </p> </blockquote> <p>I'm just starting to learn C# by writing a contrived application called Journal. In a function for parsing journal files I've declared the variable <code>DateTime currentEntryDate</code>. It won't get a value until I reach a line that defines a new entry. The <em>second</em> time I reach an entry line, the variable will be used to create an instance of class <code>JournalEntry</code> for the previous entry.</p> <p>The problem is that the code for the usage of the variable won't compile:</p> <blockquote> <p>Use of unassigned local variable 'currentEntryDate'</p> </blockquote> <p>This makes no sense to me. Do I really have to give a wasted initial value to my variables just to keep the compiler happy? Surely I've misunderstood something, or there's an error in my code somewhere.</p> <p>The code on Pastebin: <a href="http://pastebin.com/1JcqDzx4" rel="nofollow noreferrer">Journal.cs</a>. I've highlighted the relevant lines.</p> <p>The code:</p> <pre><code>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&lt;JournalEntry&gt; Entries; private static readonly string EntryLineRegex = @"-- Entry: (?&lt;title&gt;.*) \((?&lt;year&gt;\d{4})-(?&lt;month&gt;\d{2})" + @"-(?&lt;day&gt;\d{2})\)"; 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; } } } </code></pre>
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    1. CONo. But valid code *must* assign all local variables a value before they are accessed and the compiler *must* be guaranteed of this. I am certain this is a duplicate.
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    2. CO@pst: And how do I guarantee the compiler of that?
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    3. COIt's the compiler's way of ensuring that you don't use variables before they have a value. The compiler can't determine from your complicated conditional statements that `currentEntryDate` will have a value before you use it, so it throws up that error. Is giving `currentEntryDate` an initial value here such a tragedy?
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