extened options in writing new post

Disable the RTE i the Users panel. Then paste in the code. This way WP won’t strip anything.

i need that there is some thing … some tag like <–code–> which i can wrap against the code and it is interpreted as some thing which should go without processing as a markup language

You need a plugin to do that. There are many plugins for adding code snippets. I use this one: https://blog.igeek.info/wp-plugins/igsyntax-hiliter/