This guide will teach you how to prevent other users from commenting or resharing your posts on Google +. You can configure these settings for each of your individual posts.
Sign in to Google + and then click on the red Pencil button to create a new post. Click on the More menu displayed at the top right corner of the post and then tick Disable comments and Disable reshares:
Google + gives you the ability to choose who can comment on your public posts. Head to Settings > General > Who can comment on your public posts? and then click on the Manage button. Click on the drop down menu next to Who can comment on your public posts? and select the desired preset: