Adding code only to post pages

consider to use a conditional statement based on one of the conditional tags;

http://codex.wordpress.org/Conditional_Tags

http://codex.wordpress.org/Conditional_Tags#The_Main_Page

what exactly you need to use depends on where exactly you want to include your code;

this example would not show the code in single posts:

<?php if( !is_single() ) :
/*code*/;
endif; ?>

this example would show the code only on the posts page:

<?php if( is_home() ) :
/*code*/;
endif; ?>