Question

I am doing assignment 4, problem4. I totally have no idea, what's epsilon for? thanks

Answer 1

Epsilon just says how close you want the final amount to be to zero. Since you are using floats, it would take much longer to iterate until your answer is exactly 0.000000000 etc.
Instead it checks to see if the amount left is within epsilon of zero. Epsilon of 1.0 would be within $1, epsilon of 0.01 would be with 1cent, etc