Decimal

This type accurately stores numeric data. In some C# programs (like those with financial data) rounding errors are harmful—decimal helps.

Decimal stores large and small numbers with many digits after the decimal place. We access methods like decimal.Ceiling and Floor.

Memory

Decimal values require 16 bytes. The decimal type is a value type—it requires more memory than most other value types used commonly in C#.

using System;

const int _count = 1000000; // One million decimals
long bytes1 = GC.GetTotalMemory(true);

// Part 1: allocate an array of decimal values.
// ... Assign an element to make the allocation not optimized out.
decimal[] array = new decimal[_count];
long bytes2 = GC.GetTotalMemory(true);
array[1] = 0.1M;

// Part 2: compute the memory usage of the decimal type.
long difference = bytes2 - bytes1;
double per = (double)difference / _count;
Console.WriteLine("Program used: {0:0.0} MB", (double)difference / (1024 * 1024));
Console.WriteLine("Each decimal element required: {0:0.0} bytes", per);
Program used: 15.3 MB
Each decimal element required: 16.0 bytes

Operators

Decimal is a value type. It can be manipulated with the standard numeric operators in the C# language. These include the plus, minus, multiply and divide operators.

using System;

decimal d = 1.0M;
// Test decimal.
if (d == 1.0M)
{
    Console.WriteLine(d);
}
decimal y = 0.5M;
// Add decimal.
y += d;
Console.WriteLine(y);
// Subtract and multiply decimal.
y -= (d * 2);
Console.WriteLine(y);
1.0
1.5
-0.5

Constants

If you want to know the maximum or minimum value, access the MaxValue and MinValue constants. You can also use the One, Zero, and MinusOne constants.

using System;

Console.WriteLine(decimal.MaxValue);
Console.WriteLine(decimal.MinValue);
Console.WriteLine(decimal.One);
Console.WriteLine(decimal.Zero);
Console.WriteLine(decimal.MinusOne);
79228162514264337593543950335
-79228162514264337593543950335
1
0
-1

Floor, Ceiling

When using decimal, you should call methods available on the decimal class instead of those in the Math class for accuracy reasons.

using System;

Console.WriteLine(decimal.Ceiling(1.1M));
Console.WriteLine(decimal.Floor(1.1M));
2
1

Arithmetic

To improve the clarity of decimal manipulations, you can use the Add, Multiply, Subtract and Divide methods. Each of these methods receives two arguments.

using System;

Console.WriteLine(decimal.Add(1.1M, 1.3M)); // Add
Console.WriteLine(decimal.Multiply(5.0M, 2.0M)); // Five times two
Console.WriteLine(decimal.Subtract(2.0M, 1.0M)); // Two minus one
Console.WriteLine(decimal.Divide(10M, 2M)); // Ten divided by two
2.4
10.00
1.0
5

Remainder

When doing important computations with money, you may want to get the remainder of a division. The remainder is the part left over after the division completes.

using System;

// Remainder of 2 divided by 1.5 is 0.5
Console.WriteLine(decimal.Remainder(2.0M, 1.5M));
0.5

Truncate

This method erases all the numbers after the decimal place. It doesn't take into consideration whether the number would be rounded up or rounded down.

using System;

// Truncate removes the digits after the decimal place.
Console.WriteLine(decimal.Truncate(4.55M));
4

Negate

Negate makes positive decimals negative, and makes negative decimals positive. You could duplicate this functionality by multiplying by negative one.

using System;

// Makes positive numbers negative, and negative numbers positive.
Console.WriteLine(decimal.Negate(1.5M));
Console.WriteLine(decimal.Negate(-1.5M));
-1.5
1.5

Round, MidpointRounding

The decimal.Round method by default rounds down or up to the specified decimal place. You can specify the MidpointRounding to further define the required behavior.

using System;

// Round to one decimal place.
Console.WriteLine(decimal.Round(1.59M, 1));

// Demonstrate MidpointRounding enumeration.
Console.WriteLine(decimal.Round(2.5M, 0, MidpointRounding.ToEven));
Console.WriteLine(decimal.Round(2.5M, 0, MidpointRounding.AwayFromZero));
1.6
2
3

Parse, TryParse

The decimal.Parse method will throw an exception if you feed it an incorrectly-formatted value. TryParse will handle errors by returning a false value.

using System;

// Use Parse on arguments that are always correct.
decimal value = decimal.Parse("100.01");
Console.WriteLine(value);

// Use TryParse when errors are expected.
decimal value2;
if (decimal.TryParse("perl", out value2))
{
    Console.WriteLine("Not reached");
}
100.01

Convert

It is sometimes wasteful to store many decimals. You can use the "To" methods on the decimal type to convert to smaller memory representations of the number.

using System;

const decimal input = 5;
// Convert this decimal into other compatible types.
Console.WriteLine(decimal.ToByte(input));
Console.WriteLine(decimal.ToDouble(input));
Console.WriteLine(decimal.ToInt16(input));
Console.WriteLine(decimal.ToInt32(input));
Console.WriteLine(decimal.ToInt64(input));
Console.WriteLine(decimal.ToSByte(input));
Console.WriteLine(decimal.ToSingle(input));
Console.WriteLine(decimal.ToUInt16(input));
Console.WriteLine(decimal.ToUInt32(input));
Console.WriteLine(decimal.ToUInt64(input));
5
5
5
5
5
5
5
5
5
5

FromOACurrency, ToOACurrency

Decimal provides FromOACurrency and ToOACurrency. FromOACurrency receives an OA value and converts it into a decimal.

The decimal type is a powerful and accurate representation for number data in memory. It is valuable for representing important quantities like amounts of money.