计算pi的前n位？

Question

Hi i am trying to code Calculate the first n digits of pi

using System;
using System.Numerics;
namespace PiCalculator
{
    
    class Program
    {
        
        static void Main(string[] args)
        {
            System.Decimal.Precision = 5;
            Console.WriteLine("How Many Digit?");
            int n = Convert.ToInt32(Console.ReadLine());

            decimal pi = 0;
            decimal t = 0;
            decimal deno = 0;
            int k = 0;

            t=1*(Factorial(1))*(13591409+545140134*k);
            deno = ((decimal)Factorial(3*k))*((decimal)Math.Pow((double)Factorial(k),3))*((decimal)(Math.Pow(640320,(3*k))));
            pi += t/deno;
            pi = pi * 12 / (decimal)Math.Pow(640320,1.5);
            pi = 1/pi;

            Console.WriteLine(pi);
        }

        // Factorial fonksiyonu
        static decimal Factorial(int n)
        {
            if (n == 0)
                return 1;

            return n * Factorial(n - 1);
        }
    }
}

I am new on C# i need help with set Decimal.Precision pls help.

I am trying to calculate n number of pi and write it.

Code can calculate but i dont know how can write n number of this calculation result.

Answer 1

You can write out the substring of pi from 0 to n:

replace: Console.WriteLine(pi);

with: Console.WriteLine(pi.ToString().Substring(0, (n > 1)? n + 1: n));

the n + 1 logic increases the number of characters since the decimal "." does not count as a digit. Notice to increase by 1 only if user specifies more than 1 digit (n > 1).