Best Way to get Whole Number part of a Decimal Number

Question

What is the best way to return the whole number part of a decimal (in c#)? (This has to work for very large numbers that may not fit into an int).

GetIntPart(343564564.4342) >> 343564564
GetIntPart(-323489.32) >> -323489
GetIntPart(324) >> 324

The purpose of this is: I am inserting into a decimal (30,4) field in the db, and want to ensure that I do not try to insert a number than is too long for the field. Determining the length of the whole number part of the decimal is part of this operation.

Answer 1

By the way guys, (int)Decimal.MaxValue will overflow. You can't get the "int" part of a decimal because the decimal is too friggen big to put in the int box. Just checked... its even too big for a long (Int64).

If you want the bit of a Decimal value to the LEFT of the dot, you need to do this:

Math.Truncate(number)

and return the value as... A DECIMAL or a DOUBLE.

edit: Truncate is definitely the correct function!

---

Noldorin is annoyed that I changed my answer. Let me be clear here--it was Jon's comment to this question that prompted me to change my answer. I gave him credit in the comments for doing so. I have also upvoted every answer in this question that was correct. I did not select the answer, Yaakov did. I did not vote up my question, SO members did.

Here's a friendly guide to getting rep from answers.

1) Answer quickly. Fastest gun rules. You'll see high rep people here post an initial answer, only to come back and modify it if needed. If you don't like that, you don't like SO.

2) The more content you provide the more upvotes you get. While anyone posting a correct answer -- Math.Truncate -- should get upvotes, how do you pick one to be the answer? Often its chosen by upvote total (see 1). But if you provide more information than just the answer, you tend to get more upvotes. Note how I was clear about why the question was flawed--you get overflows when casting a Decimal to an int. That's an incredibly important piece of information that every developer needs to know--an unchecked build would result in hard to track down bugs that this overflow would cause. Its that extra information that helps, And people tend to upvote answers that contain that extra info.

3) If your answer is wrong, fix it. Wrong answers help nobody. The fact is that when I changed my answer, I was already the highest voted answer in here. I could have just left it; it was an acceptable answer, but not the best answer. So after I read Jon's comment I did some reading on the Truncate function. It did, of course, everything that needed to be done here. So I responded to his comment, saying he was right, and updated my answer, marking it as edited. If I'm a scumbag for changing a wrong answer to a right answer and giving credit where credit is due, then I'm a scumbag. But I'm not going to let an incorrect answer stand if I can help it.

Answer 2

You just need to cast it, as such:

int intPart = (int)343564564.4342

If you still want to use it as a decimal in later calculations, then Math.Truncate (or possibly Math.Floor if you want a certain behaviour for negative numbers) is the function you want.

Answer 3

int intPart = (int)343564564.4342;

Answer 4

Depends on what you're doing.

For instance:

//bankers' rounding - midpoint goes to nearest even
GetIntPart(2.5) >> 2
GetIntPart(5.5) >> 6
GetIntPart(-6.5) >> -6

or

//arithmetic rounding - midpoint goes away from zero
GetIntPart(2.5) >> 3
GetIntPart(5.5) >> 6
GetIntPart(-6.5) >> -7

The default is always the former, which can be a surprise but makes very good sense.

Your explicit cast will do:

int intPart = (int)343564564.5
// intPart will be 343564564

int intPart = (int)343564565.5
// intPart will be 343564566

From the way you've worded the question it sounds like this isn't what you want - you want to floor it every time.

I would do:

Math.Floor(Math.Abs(number));

Also check the size of your decimal - they can be quite big, so you may need to use a long.

Answer 5

I think System.Math.Truncate is what you're looking for.