MATLAB: Help with a simple loop

Question

% For version1, we can get the expected answer. but for version2, p==0.3 and p==0.7 give us all zeros?

% What's wrong here? Any comments are welcome!

%% compare version1 and version2

%version1
p = 0.1:0.1:0.9;
for q = 0.1:0.1:0.9
  r = (p==q)
end
%version2
p==0.2,p==0.3,p==0.7,p==0.8

Answer 1

It's discussed in the FAQ: http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F