title: Visual Studio 2010 cannot add existing item in C project
body: <p>I have the source code and hope to add the file <code>xxx.c</code> to <code>source files</code> of the project created by Visual Studio 2010. However, the source file is still in the original location even if I right click <code>add</code> ---><code>existing item</code>. What is added is actually just a link. What is the simpe way to adding the item (but not a link) to the project?</p>