Hi Beatrice, thanks for your questions. You are making a great choice to be a software engineer. I learned many skills from my USC education and I am really happy that I studied engineering.
I have listed the three majors that you mentioned with a link to their undergraduate website.
The CS major has over half its classes as coding classes. ISE has approximately 3 coding classes and ISIS computer track has approximately 5 coding classes. If you are unsure what major to pick, remember that you can always transfer into a different major once you have started school at USC. This link (http://viterbi.usc.edu/students/undergrad/handbook.htm) has links to all the majors and course requirements - click on CS, ISE, and ISIS to get a better idea of which courses and schedules look interesting.
I decided to major in ISE as an undergraduate at USC because it incorporated both engineering and management perspectives. In ISE, I learned about systems, processes, and people and how they all work together to drive innovation and technology in an organization. If I had studied CS, I would have focused more on knowledge and skills for system, hardware, and software development as well as related theories and algorithms. I am now in graduate school at Brown University, and I am studying Computer Science which builds perfectly on my ISE background.
Also, it is never too early to start coding - check out the following websites for courses or tutorials:www.codecademy.com, www.edx.org, http://girlswhocode.com, http://code.org, and www.lynda.com. Keep up the hard work and follow your engineering dream!!