Float Value Is Lost in Int

Question

Trying to cast float to int but there's something missing

float submittedAmount = 0.51f;

int amount = (int)(submittedAmount * 100);

here is watch. look at the variable values

Why is the answer 50?

this may help: http://stackoverflow.com/questions/8911440/strange-behavior-when-casting-a-float-to-int-in-c-sharp — Massimiliano Peluso, Feb 11 '13 at 09:58
You may need to apply rounding to the float before casting to an int. — Quetzalcoatl, Feb 11 '13 at 09:59

Øyvind Bråthen · Answer 1 · 2013-02-11T10:03:23.787

Because of floating point aritmethics, the multiplied value isn't exactly 51. When I tried now, *0.51f * 100* gave the result 50.9999990463257.

And when you parse 50.9999990463257 to and int, you surely get 50.

If you want calculations like this to be exact, you will have to use a type like decimal instead of float.

If you want to understand why, read the article I have linked below.

score 1 · Answer 2 · answered Feb 11 '13 at 09:58

1

Try with

int amount = (int)(submittedAmount * 100.0);

When you write 0.51f is not exactly 0.51

answered Feb 11 '13 at 09:58

Soner Gönül

2

How will changing 100 to 100.0 help? Did you read the article? ;) – Øyvind Bråthen Feb 11 '13 at 10:07

score 0 · Answer 3 · answered Feb 11 '13 at 10:00

0

Use Convert class. Otherwise the answer still will be 50.

 var amount  = Convert.ToInt32(submittedAmount * 100.0));

answered Feb 11 '13 at 10:00

Tormod

score 0 · Answer 4 · answered Feb 11 '13 at 10:01

0

0.51f is actually 0.509999999999. because floating points are imprecise.

I would like to add that, do not use float for monetary calculations. Use decimal instead.

answered Feb 11 '13 at 10:01

Aniket Inge

4 Answers4