These codes may be programming codes or just the normal codes your readers can copy and paste as gadgets.You post with codes on blogger using one of the ways listed below
Goto post with codes in blogger post using an html parser to convert the code. Paste it into the text box then select encode. Copy the parsed code into your blogger post
Another way of doing this is to Visit Hilite.me
Paste your code on source code box, You can choose optional settings like including line numbers, then click on highlight. Copy the code from the html box and paste in your blog post.