You need to ask the question (in an appropriate place, which wouldn't be
this newsgroup) as to why your C++ program got it wrong, not why Excel got
it right (assuming that your number really was 2.0).
There are problems with storing some numbers exactly if using fixed point
decimal or fixed point binary, but 2.0 can easily be stored in either of
those formats. [As examples, 1/3 can't be expressed exactly in fixed point
decimal, and 1/10 can't in fixed point binary.]
Also, if you display a number with a limited number of decimal places, then
it may of course look like a different number from what it actually is, so
if a calculation comes to 2.0000001 or 1.99999999 and you ask Excel to
display to 1 decimal place it will look like 2.0. You'll also need to
remember that precision in Excel is limited to 15 significant figures.
