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</div><h1>C# <span class="color_h1">Exceptions - Try..Catch</span></h1>
<div class="w3-clear nextprev">
<a class="w3-left w3-btn" href="cs_files.html">❮ Previous</a>
<a class="w3-right w3-btn" href="cs_howto_add_two_numbers.html">Next ❯</a>
</div>
<hr>
<h2>C# Exceptions</h2>
<p>When executing C# code, different errors can occur: coding errors made by the programmer, errors due to wrong input,
or other unforeseeable things.</p>
<p>When an error occurs, C# will normally stop and generate an error message. The technical term for this is: C# will throw an <b>exception</b> (throw an error).</p>
<hr>
<h2>C# try and catch</h2>
<p>The <code class="w3-codespan">try</code> statement allows you to define a block of code to be
tested for errors while it is being executed.</p>
<p>The <code class="w3-codespan">catch</code> statement allows you to define a block of code to
be executed, if an error occurs in the try block.</p>
<p>The <code class="w3-codespan">try</code> and <code class="w3-codespan">catch</code> keywords
come in pairs:</p>
<div class="w3-example">
<h3>Syntax</h3>
<pre class="language-csharp w3-white"><code>try
{
// <em>Block of code to try
</em>}
catch (Exception e)
{
// <em>Block of code to handle errors
</em>}</code></pre>
</div>
<p>Consider the following example, where we create an array of three integers:</p>
<div class="w3-example w3-pale-red">
<p>This will generate an error, because <strong>myNumbers[10]</strong> does not exist.</p>
<pre class="language-csharp w3-white w3-border-red"><code>int[] myNumbers = {1, 2, 3};
Console.WriteLine(myNumbers[10]); // error!</code></pre>
<p>The error message will be something like this:</p>
<div class="w3-padding notranslate w3-black w3-margin-bottom">
<code>System.IndexOutOfRangeException: 'Index was outside the bounds of the
array.' </code>
</div>
</div>
<p>If an error occurs, we can use <code class="w3-codespan">try...catch</code>
to catch the error and execute some code to handle it.</p>
<p>In the following example, we use the variable inside the catch block (<code class="w3-codespan">e</code>) together with the built-in <code class="w3-codespan">Message</code> property, which outputs a message that describes the exception:</p>
<div class="w3-example">
<h3>Example</h3>
<pre class="language-csharp w3-white"><code>try
{
int[] myNumbers = {1, 2, 3};
Console.WriteLine(myNumbers[10]);
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}</code></pre>
<p>The output will be:</p>
<div class="w3-padding notranslate w3-black">
<code>
Index was outside the bounds of the array.</code>
</div>
<a target="_blank" class="w3-btn w3-margin-bottom w3-margin-top" href="trycsd82b.html?filename=demo_try_catch_message">Try it Yourself »</a>
</div>
<p>You can also output your own error message:</p>
<div class="w3-example">
<h3>Example</h3>
<pre class="language-csharp w3-white"><code>try
{
int[] myNumbers = {1, 2, 3};
Console.WriteLine(myNumbers[10]);
}
catch (Exception e)
{
Console.WriteLine("Something went wrong.");
}</code></pre>
<p>The output will be:</p>
<div class="w3-padding notranslate w3-black">
<code>
Something went wrong.</code>
</div>
<a target="_blank" class="w3-btn w3-margin-bottom w3-margin-top" href="trycscfc7.html?filename=demo_try_catch">Try it Yourself »</a>
</div>
<hr>
<h2>Finally</h2>
<p>The <code class="w3-codespan">finally</code> statement lets you execute code, after <code class="w3-codespan">try...catch</code>, regardless of the result:</p>
<div class="w3-example">
<h3>Example</h3>
<pre class="language-csharp w3-white"><code>try
{
int[] myNumbers = {1, 2, 3};
Console.WriteLine(myNumbers[10]);
}
catch (Exception e)
{
Console.WriteLine("Something went wrong.");
}
finally
{
Console.WriteLine("The 'try catch' is finished.");
}
</code></pre>
<p>The output will be:</p>
<div class="w3-padding notranslate w3-black">
<code>
Something went wrong.<br>
The 'try catch' is finished.
</code>
</div>
<a target="_blank" class="w3-btn w3-margin-bottom w3-margin-top" href="trycs73d2.html?filename=demo_try_catch_finally">Try it Yourself »</a>
</div>
<hr>
<h2>The throw keyword</h2>
<p>The <code class="w3-codespan">throw</code> statement allows you to create a custom error.</p>
<p>The <code class="w3-codespan">throw</code> statement is used together with an <strong>exception class</strong>. There are many exception classes available in C#: <code class="w3-codespan">ArithmeticException</code>,
<code class="w3-codespan">FileNotFoundException</code>, <code class="w3-codespan">
IndexOutOfRangeException</code>, <code class="w3-codespan">TimeOutException</code>, etc:</p>
<div class="w3-example">
<h3>Example</h3>
<pre class="language-csharp w3-white"><code>static void checkAge(int age)
{
if (age < 18)
{
throw new ArithmeticException("Access denied - You must be at least 18 years old.");
}
else
{
Console.WriteLine("Access granted - You are old enough!");
}
}
static void Main(string[] args)
{
checkAge(15);
}</code></pre>
<p>The error message displayed in the program will be:</p>
<div class="w3-padding notranslate w3-black">
<code>
System.ArithmeticException: 'Access denied - You must be at least 18 years old.'
</code>
</div>
<br>
</div>
<p>If <code class="w3-codespan">age</code> was 20, you would <strong>not</strong> get an exception:</p>
<div class="w3-example">
<h3>Example</h3>
<pre class="language-csharp w3-white"><code>checkAge(20);</code></pre>
<p>The output will be:</p>
<div class="w3-padding notranslate w3-black">
<code>
Access granted - You are old enough!
</code>
</div>
<a target="_blank" class="w3-btn w3-margin-bottom w3-margin-top" href="trycs72b8.html?filename=demo_throw">Try it Yourself »</a>
</div>
<!--
<hr>
<h2>Many Exceptions</h2>
<p>You can define as many <code class="w3-codespan">catch</code> blocks as you want:</p>
<div class="w3-example">
<h3>Syntax</h3>
<div class="w3-code notranslate javaHigh">
try {<br>
// <em>Block of code to try<br>
</em>}<br>
catch(ExceptionType1 <em>e1</em>) {<br>
// <em>Block of code to handle errors<br>
</em>}<br>catch(ExceptionType2 <em>e2</em>) {<br>
// <em>Block of code to handle errors<br>
</em>}
<br>catch(ExceptionType3 <em>e3</em>) {<br>
// <em>Block of code to handle errors<br>
</em>}</div>
</div>
-->
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