How to fix rounding error

Question

I am getting this out put from the code which will follow:

49

49.000000000000000000000000001

I want to know how to fix it so I get back to 49.

decimal a = 49;
decimal b = 24;

decimal result = a / b;

decimal c = result * b;

Console.WriteLine(a);
Console.WriteLine(c);

the windows 10 calculator app get it right and its using more precision I guess. There has to be a way to fix this?

Possible duplicate of [Is floating point math broken?](http://stackoverflow.com/questions/588004/is-floating-point-math-broken) — r3mainer, May 21 '17 at 18:23
Are you sure that windows app doesn't just round it? Good question non the less. — Karolis Kajenas, May 21 '17 at 18:31
Relevant http://stackoverflow.com/questions/618535/difference-between-decimal-float-and-double-in-net — DavidG, May 21 '17 at 18:35

Rufus L · Accepted Answer · 2017-05-21T18:43:57.320

1

I think you actually want a lower precision type to do the math. If you use a double type, it works fine:

double a = 49;
double b = 24;

double result = a / b;
double c = result * b;

Console.WriteLine(a);
Console.WriteLine(c);

edited May 21 '17 at 18:43

answered May 21 '17 at 18:34

Rufus L

36,127
5
30
43

score -2 · Answer 2 · answered May 21 '17 at 18:33

-2

Instead of using one number to store a quotient, use two numbers to store a quotient.

decimal a = 49;
decimal b = 24;

decimal resultNumerator = a;
decimal resultDenominator = b;

decimal c = (resultNumerator * b) / resultDenominator;

Console.WriteLine(a);
Console.WriteLine(c);

answered May 21 '17 at 18:33

John Pick

5,562
31
31

1

What! No. Sorry. – John May 21 '17 at 18:48
Also, what is the point of `resultNumerator` and `resultDenominator`? This doesn't answer the question at all. – DavidG May 21 '17 at 18:51
If you postpone all division operations until it's time to display a result, the precision problem disappears. – John Pick May 22 '17 at 20:30

How to fix rounding error

2 Answers2