Answer from cs61c-ee (Michael Shen 15963205) for Question 4
Because you have no "#n"s preceding each assignment, both assignments in the block will be executed simultaneously.
Because the code executes the code simultaneously, it may choose any combination of the variables.  
The code might want to assign s=0 and then do a=1 and b=0 from the second line to give you something you don't expect. Or the code might mean s=0; a=1; and b=1; which has has no expected value assigned to it.