
How to avoid wrong answers in simple arithmetic expressions.
Posted:
Jan 19, 2013 2:04 AM


I tried the following cody problem for fun: [quot] Given an amount of currency, return a vector of this form:
[100 50 20 10 5 2 1 0.5 0.25 0.1 0.05 0.01]
Example:
Input a = 257.68 Output b is [2 1 0 0 1 1 0 1 0 1 1 3]
Always use bigger bills/coins if possible. [/quot]
My solution: function b = makingChange(a) v = [100 50 20 10 5 2 1 0.5 0.25 0.1 0.05 0.01]; for i = 1 : length(v) b(i) = floor(a/v(i)); a = a  b(i)*v(i); end end
But, due to rounding error, this gives a wrong answer for example for a = 135.01. The problem does not go away even if I replace the last line by a = rem(a, v(i)). How does one avoid such issues in general?

