NOTE: This bit of code is potentially very dangerous and should NOT be uploaded to your web host. I only use this function on my localhost to quickly check that a snippet of code works.
If you want to quickly run some PHP code, and don't want to have to go through creating a file just to see the outcome of a simple calculation is then this snippet might be of some use to you.
It works by taking the contents of the textarea and creating a file with the filename of 'tempcodefile.php', which contains that code. The created file is then included in order to run the code, the output of which is displayed at the top of the screen.