echo username into code

Hi,
I am currently fiddling round with the latest posts by author plugin.

At present, you can put the plugin into the theme pages by using <?php echo do_shortcode('[latestbyauthor author="username" show="3"]'); ?> This requires you to manually input the authors username.

I am trying to automate this setting the user name based on the users profile you are viewing – here is the user profile page for reference: http://www.copymusic.co.uk/COPYmusicscout2/

Now I am familiar with how to pull the relevent users name, as I have used the following code to correctly display the “view uploads by xxxxx” link. I have been using the following: <?php echo $user->screenname; ?>.

I therefore tried using <?php echo do_shortcode('[latestbyauthor author="<?php echo $user->screenname; ?>" show="3"]'); ?> which didn’t work.

I read something online which suggested the 2nd echo wasn’t required so I tried <?php echo do_shortcode('[latestbyauthor author=" $user->screenname" show="3"]'); ?> which again didn’t work.

I am therefore a little stuck . . At the moment it is just displaying the last few posts onto the site, I have fiddle around manually inputting the relevent user name and it does work, but obviously shows the same posts regardless of user profile!

I am pretty familiar with some PHP so can take simple instructions, unfortunately I am a bit stuck at this time!

Any suggestions will be greatly appreciated, if you need any more detail, please let me know!

Many thanks
Ryan