Create a post that writes a string

I would like to create a blog entry that writes a string, so that everytime someone goes to the page it will write the string, so that farther down on the page it will use the data that was written as of the comment form. This is what I have tried using so far as code in the blog entry:

—begin code—-

<?php
$my_string = “This is the string I want to save”;
?>

–end code—

… but it keeps posting it just as plain text instead of entering it as code. What’s the deal? Any help is greatly appreciated.