its pretty simple...
Consider the outermost for loop
for z=2 x reaches 3
now apply x++ (because "if" condition is evaluated to be true by
Short circuit evaluation)
so at this point z=2, x=4 and y=2
similarly when z=3, x=6 and y=2
and finally z=4, x=8 and y=2
the basic idea is once z reaches 2, x increments twice (++x and x++) for every value of z