算术运算得出错误结果

Question

I might be missing something very basic here. But I don't know how to figure out that basic thing. When I set T to 10 and dt to 0.1, I should get the result 101 but I am getting the result as 100. Why is it so?

n_sim_steps = (int)(T/dt) + 1

Furthermore, if I execute this as a watch in eclipse, it returns 101, but in code it results in 100.

Answer 1

It should be

n_sim_steps = (int)(T/dt + 0.5) + 1

You are a victim of precission loss

10 / 0.1 may be 99.999999999999 because of this loss and may be casted back to int as 99 . Adding 0.5 and then casting would make sure that the result is rounded.

Answer 2

You better to use ceil function.

function signature

double ceil (double x);

like ceil(2.3) will results 3