Question

How do I tell if a decimal or double value is an integer?

For example:

decimal d = 5.0; // Would be true
decimal f = 5.5; // Would be false

or

double d = 5.0; // Would be true
double f = 5.5; // Would be false

The reason I would like to know this is so that I can determine programmatically if I want to output the value using .ToString("N0") or .ToString("N2"). If there is no decimal point value, then I don’t want to show that.

Answer 1

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)