Computer programs (software) are protected by copyright. Copying and distributing software is therefore not permitted without the copyright holder's permission. However, the copyright only applies to the bron code and/or object code as such. The code does not include the functionality, programming language and associated file formats. They are purely functional and are therefore not protected by copyright.
As a programmer, you don't need to take any formal action to have your software protected by copyright. In that respect, there is no difference with books, articles, films and so on. Your copyright arises by operation of law. However, always be aware that not all parts of the software are copyrighted.
There are many software licences. Many of these licences allow researchers very little room for manoeuvre, but some give more freedom to use and reuse licenced software.