How to Determine If a Decimal/Double Is an Integer

How to determine if a decimal/double is an integer?

For floating point numbers, n % 1 == 0 is typically the way to check if there is anything past the decimal point.

public static void Main (string[] args)
{
    decimal d = 3.1M;
    Console.WriteLine((d % 1) == 0);
    d = 3.0M;
    Console.WriteLine((d % 1) == 0);
}

Output:

False
True

Update: As @Adrian Lopez mentioned below, comparison with a small value epsilon will discard floating-point computation mis-calculations. Since the question is about double values, below will be a more floating-point calculation proof answer:

Math.Abs(d % 1) <= (Double.Epsilon * 100)

How to test if a double is an integer

if ((variable == Math.floor(variable)) && !Double.isInfinite(variable)) {
    // integer type
}

This checks if the rounded-down value of the double is the same as the double.

Your variable could have an int or double value and Math.floor(variable) always has an int value, so if your variable is equal to Math.floor(variable) then it must have an int value.

This also doesn't work if the value of the variable is infinite or negative infinite hence adding 'as long as the variable isn't inifinite' to the condition.

How can I accurately determine if a double is an integer?

double can store an exact representation of certain values, such as small integers and (negative or positive) powers of two.

If it does indeed store an exact integer, then ((int)d == d) works fine. And indeed, for any 32-bit integer i, (int)((double)i) == i since a double can exactly represent it.

Note that for very large numbers (greater than about 2**52 in magnitude), a double will always appear to be an integer, as it will no longer be able to store any fractional part. This has implications if you are trying to cast to a Java long, for instance.

What's a good way to check if a double is an integer in C#?

return Math.Truncate(number) == number;

As mentioned in the comments, you might need to take account of the fact that a double representation of your number might not be an exact integer. In that case you'll need to allow for some margin-of-error:

double diff = Math.Abs(Math.Truncate(number) - number);
return (diff < 0.0000001) || (diff > 0.9999999);

Checking if a double value is an integer - Swift

Try 'flooring' the double value then checking if it is unchanged:

let dbl = 2.0
let isInteger = floor(dbl) == dbl // true

Fails if it is not an integer

let dbl = 2.4
let isInteger = floor(dbl) == dbl // false

How to check if a double value has no decimal part

You could simply do

d % 1 == 0

to check if double d is a whole.

Check if a number has a decimal place/is a whole number

Using modulus will work:

num % 1 != 0
// 23 % 1 = 0
// 23.5 % 1 = 0.5

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Note that this is based on the numerical value of the number, regardless of format. It treats numerical strings containing whole numbers with a fixed decimal point the same as integers:

'10.0' % 1; // returns 0
10 % 1; // returns 0
'10.5' % 1; // returns 0.5
10.5 % 1; // returns 0.5

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