MATLAB: Does the if statement in this while loop not work

Question

t=0;  
dt=0.1;  
dd=0.1;  
i=0;  
while t<=2  
    t=t+dt;
    if t==dd
        i=i+1;
        dd=dd+0.1;
    end    
end
fprintf('%f \n',i)

It should print that i is 20, however it prints that it is 0.

I also tried to use rem, but it gives that i is 3

t=0;  
dt=0.01;  
dd=0.1;  
i=0;  
while t<=2  
    t=t+dt;
    if rem(t,dd)==0
        i=i+1;
        dd=dd+0.1;
    end    
end
fprintf('%f \n',i)

Thanks

Answer 1

"It should print that i is 20, however it prints that it is 0"

Not in the world of floating point numbers. Never use exact equivalence (i.e. ==) to test if decimal values are the same: always compare the absolute difference against a tolerance:

abs(A-B)<tol

You need to learn about the practical limits of floating point numbers:

http://www.mathworks.com/help/matlab/matlab_prog/floating-point-numbers.html

http://www.mathworks.com/matlabcentral/answers/69-why-does-1-2-3-1-3-not-equal-zero

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

http://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

http://www.mathworks.com/matlabcentral/answers/41536-why-is-2-24-10-22-4-not-equal-to-0

https://www.mathworks.com/matlabcentral/newsreader/view_thread/66553

http://www.mathworks.com/company/newsletters/news_notes/pdf/Fall96Cleve.pdf

http://blogs.mathworks.com/loren/2006/08/23/a-glimpse-into-floating-point-accuracy/

http://www.mathworks.com/help/fixedpoint/ug/floating-point-numbers.html

And some external links on this topic:

http://www.lahey.com/float.htm

http://matlabgeeks.com/tips-tutorials/floating-point-comparisons-in-matlab/