C# Decimal and Money

How it works

decimal represents base-ten values with a finite precision and range. It is useful for many money calculations because common decimal fractions can be represented exactly, but it does not decide taxation, currency units or rounding policy. The m suffix makes a literal decimal rather than double. Round at the boundary required by the business rule, not repeatedly after every intermediate operation. Format with an explicit culture when a test or exported record requires one stable representation.

Run it locally

Use the .NET 10 SDK with C# 14 in a separate console lab. Create an empty project once with dotnet new console --framework net10.0, then replace Program.cs with this complete source and add any supporting files shown. Keep only one lesson entry point in the project. C# does not currently run in Bhylu’s browser playground. Apache, PHP and MySQL are not needed.

dotnet build -p:LangVersion=14.0 -p:Nullable=enable -p:TreatWarningsAsErrors=true
dotnet run --no-build

Use the SDK’s project workflow; the review compiles against its matching reference assemblies and executes the results without external NuGet packages. File-writing examples belong in a private empty lab directory.

Download the complete C# source as Program.cs.

Example

using System;
using System.Globalization;

internal static class Program
{
    private static void Main(string[] args)
    {
        decimal fee = 12.50m;
        int attendees = 3;
        decimal total = fee * attendees;
        Console.WriteLine(total.ToString("F2", CultureInfo.InvariantCulture));
        decimal rounded = Math.Round(2.345m, 2, MidpointRounding.AwayFromZero);
        Console.WriteLine(rounded.ToString("F2", CultureInfo.InvariantCulture));
    }
}

Expected result

37.50
2.35

The total has two decimal places in its display and the explicit rounding policy moves the midpoint away from zero. Another domain might require ties-to-even or rounding at invoice level. Decimal can still overflow or require rounding for division, so a financial data model must state its maximum amounts and accepted scale.