Question

Well, the rule “For money, always decimal” isn’t applied inside the Microsoft development team, because if it was:

Namespace: Microsoft.VisualBasic
Assembly:  Microsoft.VisualBasic (in Microsoft.VisualBasic.dll)

Financial.IPmt and all the other methods would receive/return decimal and not double as it is.

Now I wonder if I can use these methods without worry with round mistakes?

Should I use some other libraries to work with finances? If yes, could you point me some good ones (for C# use) ?

Answer 1

You can use this class:

public class Financial
{
    #region Methods

    public static decimal IPmt(decimal Rate, decimal Per, decimal NPer, decimal PV, decimal FV, FinancialEnumDueDate Due)
    {
        decimal num;
        if (Due != FinancialEnumDueDate.EndOfPeriod)
        {
            num = 2;
        }
        else
        {
            num = 1;
        }
        if ((Per <= 0) || (Per >= (NPer + 1)))
        {
            //Argument_InvalidValue1=

            throw new ArgumentException("Argument 'Per' is not a valid value.");
        }
        if ((Due != FinancialEnumDueDate.EndOfPeriod) && (Per == 1))
        {
            return 0;
        }
        decimal pmt = Pmt(Rate, NPer, PV, FV, Due);
        if (Due != FinancialEnumDueDate.EndOfPeriod)
        {
            PV += pmt;
        }
        return (FV_Internal(Rate, Per - num, pmt, PV, FinancialEnumDueDate.EndOfPeriod) * Rate);
    }

    public static decimal PPmt(decimal Rate, decimal Per, decimal NPer, decimal PV, decimal FV, FinancialEnumDueDate Due)
    {
        if ((Per <= 0) || (Per >= (NPer + 1)))
        {
            throw new ArgumentException("Argument 'Per' is not valid.");
        }
        decimal num2 = Pmt(Rate, NPer, PV, FV, Due);
        decimal num = IPmt(Rate, Per, NPer, PV, FV, Due);
        return (num2 - num);
    }

    static decimal FV_Internal(decimal Rate, decimal NPer, decimal Pmt, decimal PV, FinancialEnumDueDate Due)
    {
        decimal num;
        if (Rate == 0)
        {
            return (-PV - (Pmt * NPer));
        }
        if (Due != FinancialEnumDueDate.EndOfPeriod)
        {
            num = 1 + Rate;
        }
        else
        {
            num = 1;
        }
        decimal x = 1 + Rate;
        decimal num2 = (decimal)Math.Pow((double)x, (double)NPer);
        return ((-PV * num2) - (((Pmt / Rate) * num) * (num2 - 1)));
    }

    static decimal Pmt(decimal Rate, decimal NPer, decimal PV, decimal FV, FinancialEnumDueDate Due)
    {
        decimal num;
        if (NPer == 0)
        {
            throw new ArgumentException("Argument NPer is not a valid value.");
        }
        if (Rate == 0)
        {
            return ((-FV - PV) / NPer);
        }
        if (Due != FinancialEnumDueDate.EndOfPeriod)
        {
            num = 1 + Rate;
        }
        else
        {
            num = 1;
        }
        decimal x = Rate + 1;
        decimal num2 = (decimal)Math.Pow((double)x, (double)NPer);
        return (((-FV - (PV * num2)) / (num * (num2 - 1))) * Rate);
    }

    #endregion Methods
}