Programs from the course Systematic Program Design: https://learning.edx.org/course/course-v1:UBCx+SPD1x+2T2015 along with exercises from the book How to Design Programs, 2nd edition: https://htdp.org/
Note: The files must be downloaded and opened with Dr Racket , otherwise, you'll see the file in DrRacket editor format, which is an unreadable format, meant to be read in by the DrRacket application. Once you open it there, then you'll be able to see the code properly.