Usually when I want to give credit to a software or code that I have used I cite the paper that describes the that software or code.
Another point: if you attribute a DOI to your code, that could result in it "stealing" the citations from a paper that describe that code.
For instance I used Intel Pintools and they specify in their FAQ[1] : I used Pin for my latest paper. What citation should I include? [actual paper here]
[1] http://writers.stackexchange.com/questions/7797/what-is-the-...
[2] http://integrity.mit.edu/writing-code
[3] http://software.ac.uk/so-exactly-what-software-did-you-use
[4] http://uark.libguides.com/content.php?pid=155080&sid=1780817
[5] https://owl.english.purdue.edu/owl/resource/560/10/
[6] https://owl.english.purdue.edu/owl/resource/560/25/
[7] And many, many more at: http://lmgtfy.com/?q=citing+source+code. I apologize for the snark, but it is a not-too-abstruse and rather common question that is very easy to figure out online without any special or prior expertise; and so I think contributes very little to the discussion.