Decimal Structure

The Decimal value type represents decimal numbers ranging from positive 79,228,162,514,264,337,593,543,950,335 to negative 79,228,162,514,264,337,593,543,950,335. The Decimal value type is appropriate for financial calculations requiring large numbers of significant integral and fractional digits and no round-off errors. The Decimal type does not eliminate the need for rounding. Rather, it minimizes errors due to rounding. For example, the following code produces a result of 0.9999999999999999999999999999 rather than 1.

decimal dividend = Decimal.One;
decimal divisor = 3;
// The following displays 0.9999999999999999999999999999 to the console
Console.WriteLine(dividend/divisor * divisor);   

When the result of the division and multiplication is passed to the Round method, the result suffers no loss of precision as the following code shows.

decimal dividend = Decimal.One;
decimal divisor = 3;
// The following displays 1.00 to the console
Console.WriteLine(Math.Round(dividend/divisor * divisor, 2));   

A decimal number is a floating-point value that consists of a sign, a numeric value where each digit in the value ranges from 0 to 9, and a scaling factor that indicates the position of a floating decimal point that separates the integral and fractional parts of the numeric value.

The binary representation of a Decimal value consists of a 1-bit sign, a 96-bit integer number, and a scaling factor used to divide the 96-bit integer and specify what portion of it is a decimal fraction. The scaling factor is implicitly the number 10, raised to an exponent ranging from 0 to 28. Therefore, the binary representation of a Decimal value is of the form, ((-296 to 296) / 10(0 to 28)), where -296-1 is equal to MinValue, and 296-1 is equal to MaxValue.

The scaling factor also preserves any trailing zeroes in a Decimal number. Trailing zeroes do not affect the value of a Decimal number in arithmetic or comparison operations. However, trailing zeroes can be revealed by the ToString method if an appropriate format string is applied.

Conversion Considerations

The following code example demonstrates the use of Decimal.

	/// <summary>
	/// Keeping my fortune in Decimals to avoid the round-off errors.
	/// </summary>
	class PiggyBank {
		protected decimal MyFortune;

		public void AddPenny() {
			MyFortune = Decimal.Add(MyFortune, .01m);
		}

		public decimal Capacity {
			get {
				return Decimal.MaxValue;
			}
		}

		public decimal Dollars {
			get {
				return Decimal.Floor(MyFortune);
			}
		}

		public decimal Cents {
			get {
				return Decimal.Subtract(MyFortune, Decimal.Floor(MyFortune));
			}
		}

		public override string ToString() {
			return MyFortune.ToString("C")+" in piggy bank";
		}
	}

.NET Framework

.NET Framework Client Profile

Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

All members of this type are thread safe. Members that appear to modify instance state actually return a new instance initialized with the new value. As with any other type, reading and writing to a shared variable that contains an instance of this type must be protected by a lock to guarantee thread safety.

Caution
Assigning an instance of this type is not thread safe on all hardware platforms because the binary representation of that instance might be too large to assign in a single atomic operation.

Reference