using System;

public class Program

{

    public static void Main()

    {

        double principal = 1000;

        double year = 0;

        double principalWithInterest = 0;

        Console.WriteLine(string.Format("Value is {0}:", CompoundInterest(1000, .025, 1, 5)));

        while(!IsPrincipalDoubled(principal, principalWithInterest)) {

            year++;

            principalWithInterest = CompoundInterest(principal, 0.025, 1, year);

            Console.WriteLine(string.Format("Year {0:0}, {1:C2}", year, principalWithInterest));

        }

        Console.WriteLine("Application Exit");

    }

    static bool IsPrincipalDoubled(double principal, double principalWithInterest) 

    {

        return (principalWithInterest - principal) / principal >= 1;

    }

​

    static double CompoundInterest(double principal,

        double interestRate,

        int timesPerYear,

        double years)

    {

        // (1 + r/n)

        double body = 1 + (interestRate / timesPerYear);

​

        // nt

        double exponent = timesPerYear * years;

​

        // P(1 + r/n)^nt

        return principal * Math.Pow(body, exponent);

    }

}

​