Some Useful Integer Helper Methods In .NET

Recently, I discovered several helper integer methods that I had never noticed before, making code much easier to read and understand.

Even Number Detection

Typically, you would do it like this:

var input = 7;

if (input % 2 == 0)
    Console.WriteLine($"{input} is even");
else
    Console.WriteLine($"{input} is odd");

Here, we use modulus division to detect whether there is a remainder after dividing by 2. If there isn’t - the number is odd.

This can be rewritten as follows using the int.IsEvenInteger method.

if (int.IsEvenInteger(input))
    Console.WriteLine($"{input} is even");
else
    Console.WriteLine($"{input} is odd");

Much easier to scan through and understand, even for a junior developer or a developer for whom C# is not their native language.

Odd Number Detection

This is a minor alteration of the above.

Traditionally you would do it this way, a negation of the even logic:

if (input % 2 != 0)
    Console.WriteLine($"{input} is odd");
else
    Console.WriteLine($"{input} is even");

You can rewrite this to use the int.IsOddInteger method

if (int.IsOddInteger(input))
    Console.WriteLine($"{input} is odd");
else
    Console.WriteLine($"{input} is even");

Positive Number Detection

Similarly, to check if a number is positive we would typically do it this way:

if (input > 0)
    Console.WriteLine($"{input} is positive");
else
    Console.WriteLine($"{input} is negative");

You can rewrite this to use the int.IsPositive method:

if (int.IsPositive(input))
    Console.WriteLine($"{input} is positive");
else
    Console.WriteLine($"{input} is negative");

Negative Number Detection

This is, again, a slight tweak of the code for positive detection.

Typically we’d do it as follows:

if (input < 0)
    Console.WriteLine($"{input} is negative");
else
    Console.WriteLine($"{input} is positive");

We can rewrite this to use the int.IsNegative method:

if (int.IsNegative(input))
    Console.WriteLine($"{input} is negative");
else
    Console.WriteLine($"{input} is positive");

Power Of Two Detection

Detecting if a number is a power of two requires a bit more thought.

A simple a algorithm is as follows:

1. Get the log of the number in base 2
2. If it is a whole number, it must be a power of two.

bool IsPowerOfTwo(int value)
{
    return Math.Log2(value) % 1 == 0;
}

There is a subtle bug here because zero will also return true, and zero is not a power of 2. We can fix that as follows:

bool IsPowerOfTwo(int value)
{
    return value > 0 && Math.Log2(value) % 1 == 0;
}

You can avoid writing your own method and use the int.Pow2 method like so:

Console.WriteLine(int.IsPow2(8));

Over and above saving you writing code, this method is faster than our algorithm above, as it uses bitwise operations for this check.

The code for int.Pow2 is as follows:

[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static bool IsPow2(int value) => (value & (value - 1)) == 0 && value > 0;

The logic here is as follows:

1. Take a number, and express it in binary
2. Subtract one from that number, and express it in binary
3. Perform a bitwise AND for each corresponding digit of the two numbers

For powers of two, this computation returns all zeros.

Take 16 and 15:

	10000
	01111

If you do a bitwise AND of each corresponding digit, and the first number is a power of two, the result will be zero.

As a bonus, these methods are also available for decimal and float types.

The code is in my GitHub.

Happy hacking!