15-110 provides a basic understanding of what computer science is. You hardly code anything, more so just learn to understand different concepts / data structures.
15-112 is rigorous python coding: you will come out with a fairly advanced understanding of python.
Take a look at the schedules:
15-110: http://www.cs.cmu.edu/~15110/schedule/
15-112: http://www.cs.cmu.edu/~112/schedule.html
I never took 18-100 so i can’t comment on that.