Studying coding during your gap year is a great idea. One of my son's friends (a high school senior) has learned coding and now has a part-time job that pays far more than the typical teenager earns after school. A young woman I know, who received a bachelor's degree in digital media from a well-regarded US university, taught herself coding after graduation and then landed her dream job because of it. Studying coding is also a smart plan because it will show effort and initiative and it will be something you do on your own (or in a classroom with others) but not part of a pricey “program" aimed at gap-year students. College admission officials see a lot of such organized gap year “programs"—expensive group travel and “volunteer" activities. While these can certainly be valuable experiences for the participants, they usually don't help to distinguish an applicant from other “gappers."
But, when it comes to US college admissions, because you are an international student, the way that you spend your gap year will not impact your admission chances as much as several other factors will. These are: