C# / .NET - Math.PI property example

The Math.PI property returns π number (3.141592653589793...).

using System;

class Program
{
    static void Main(string[] args)
    {
        // ------------------------------------------------------
        // Math.PI value priting:

        Console.WriteLine(Math.PI); // 3.141592653589793

        // ------------------------------------------------------
        // Math.PI with circle:

        double radius = 5;

        // 1. Circle surface area:
        double area = Math.PI * Math.Pow(radius, 2);
        Console.WriteLine(area); // 78.53981633974483

        // 2. Circle circumference:
        double circumference = 2 * Math.PI * radius;
        Console.WriteLine(circumference); // 31.41592653589793
    }
}

1. Documentation

namespace System
{
    public static class Math
    {
        // ...
        public const double PI = 3.1415926535897931;
        // ...
    }
}

2. Nilakantha series example

To calculate PI number Nilakantha series can be used.

using System;

public class Program
{
    static double ComputePi(int iterations)
    {
        double approximation = 3;

        double a = 2;
        for (int i = 0; i < iterations; i++)
        {
            approximation += 4 / (a * (++a) * (++a));
            approximation -= 4 / (a * (++a) * (++a));
        }
        return approximation;
    }

    public static void Main(string[] args) 
    {
        Console.WriteLine( ComputePi(    1 )); // 3.1333333333333333
        Console.WriteLine( ComputePi(    2 )); // 3.1396825396825396
        Console.WriteLine( ComputePi(    5 )); // 3.1414067184965018
        Console.WriteLine( ComputePi(   10 )); // 3.141565734658547
        Console.WriteLine( ComputePi(   20 )); // 3.141589028940776
        Console.WriteLine( ComputePi(   50 )); // 3.1415924109719824
        Console.WriteLine( ComputePi(  100 )); // 3.141592622804848
        Console.WriteLine( ComputePi(  200 )); // 3.1415926497127264
        Console.WriteLine( ComputePi(  500 )); // 3.141592653340544
        Console.WriteLine( ComputePi( 1000 )); // 3.141592653558594
        Console.WriteLine( ComputePi( 2000 )); // 3.141592653585895
        Console.WriteLine( ComputePi( 5000 )); // 3.141592653589538
    }
}

References

1. Pi - Wikipedia