# Floating point substraction

if $$x=1.0e38=1.0 * 10^{38}$$ and $$y=3.0$$
i want to find $$(x-x)+y$$ and $$(x+y)-x$$
i think the value of (x-x)+y will be just substract $$x-x=0 + y=3.0 = 3.0$$
but how can i perfom addition of different base? $$(x+y)-x$$
i think the idea is addition $$(x+y)$$ then substract $$-x$$ using floating point, i tried to convert $$y=3.0$$ to binary such as $$1.1 * 2^1$$
but how about $$10^{38}$$ to binary ?