C# 0 The Complete Reference

Pow( )

 requires 

double

 arguments, the interest rate and the number of years are 

held in 

double

 values. The future value and initial investment use the 

decimal

 type.

/* Compute the initial investment needed to attain

   a known future value given annual rate of return

   and the time period in years. */

using System;

class InitialInvestment {

  static void Main() {

    decimal initInvest; // initial investment

    decimal futVal;     // future value

    double numYears;    // number of years

    double intRate;     // annual rate of return as a decimal

    string str;

    Console.Write("Enter future value: ");

    str = Console.ReadLine();

    try {

      futVal = Decimal.Parse(str);

    } catch(FormatException exc) {

      Console.WriteLine(exc.Message);

      return;

    }

    Console.Write("Enter interest rate (such as 0.085): ");

    str = Console.ReadLine();

    try {

      intRate = Double.Parse(str);

    } catch(FormatException exc) {

      Console.WriteLine(exc.Message);

      return;

    }

    Console.Write("Enter number of years: ");

    str = Console.ReadLine();

    try {

      numYears = Double.Parse(str);

    } catch(FormatException exc) {

      Console.WriteLine(exc.Message);

      return;

    }

    initInvest = futVal / (decimal) Math.Pow(intRate+1.0, numYears);

    Console.WriteLine("Initial investment required: {0:C}",

                      initInvest);

  }

}

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