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    <p>Unless you specify <code>ref</code> or <code>out</code>, parameters are passed by value. For reference types, that means a <em>reference</em> to the object (the <code>List&lt;int&gt;</code> in this case) is passed by value.</p> <p>"Pass by value" means that the <em>argument</em> (the expression in the calling statement) is evaluated, and then the resulting value is copied into the <em>parameter</em> (the variable listed in the method signature). Any further changes to the parameter, in terms of assigning it a new value, are <em>not</em> seen by the caller. (But keep reading...)</p> <p>That means that in your first method call:</p> <pre><code>public static void SampleMethod1(List&lt;int&gt; i) { List&lt;int&gt; j = new List&lt;int&gt;(); j.Insert(0,20); i = j; } </code></pre> <p>you're creating a new list, inserting a value into it, and then copying the reference to that new list to <code>i</code> - but that has <em>no effect at all</em>. The parameter is effectively just another local variable - a change to the value of the variable itself doesn't affect the caller.</p> <p>Now compare that with your second method:</p> <pre><code>public static void SampleMethod2(List&lt;int&gt; i) { List&lt;int&gt; j = new List&lt;int&gt;(); j = i; j.Insert(0, 20); } </code></pre> <p>This creates a new list and then immediately ignores it, instead assigning the reference to the list passed in (as <code>i</code>) to <code>j</code>. It then inserts a value into the list. The net result of this method is that a value is inserted into the list. It's equivalent to:</p> <pre><code>public static void SampleMethod2(List&lt;int&gt; i) { i.Insert(0, 20); } </code></pre> <p>Note that this is <em>not</em> changing the value of the parameter. It's making a change to the object that the value of the parameter refers to. This is a <em>crucial</em> difference to understand.</p> <p>I have an article on <a href="http://pobox.com/~skeet/csharp/parameters.html" rel="noreferrer">parameter passing</a> and another one on <a href="http://pobox.com/~skeet/csharp/references.html" rel="noreferrer">reference and value types</a> which may help you understand this more.</p>
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    1. COThanks for your quick response,if so then shouldn't SampleMethod2() also give me same result as SampleMethod1()?
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    2. CO@Ardentaj: No - calling `SampleMethod1` does *nothing* to the list that's passed in, because the `Insert` method is called on the list created within the method. `SampleMethod2` will insert the value into the list that is passed in.
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    3. COThanks Jon...I will go through your articles and do you suggest any free memory profilers so that I can seethe memory allocations
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