How to show the number of each post has been read in a while loop?

the_views() is not a built in function of WordPress. In fact, WordPress does not, by default, log the number of views of posts.

There are probably several plug-ins that exist which add this functionality. The only one I have ever used (and its one I’ve never had any problems with) is WP-Postviews http://wordpress.org/extend/plugins/wp-postviews/.