Decimal type in C#

The decimal type in C# is a 128-bit data type designed for financial and monetary calculations that require high precision. Unlike float and double, the decimal type provides exact decimal representation without rounding errors, making it ideal for applications involving currency and precise arithmetic operations.

Syntax

Following is the syntax for declaring decimal variables −

decimal variableName = value;
decimal variableName = valueM; // M or m suffix required for literals

The M or m suffix is required when assigning decimal literals to distinguish them from double values −

decimal price = 19.99M;
decimal total = 0.0m;

Key Properties of Decimal Type

• Size: 128 bits (16 bytes)

• Range: ±1.0 × 10^-28 to ±7.9228 × 10²⁸

• Precision: 28-29 significant decimal digits

• Default value: 0.0M

• Suffix: M or m (mandatory for literals)

Using Decimal Arithmetic Operations

The decimal type supports all standard arithmetic operators: addition (+), subtraction (-), multiplication (*), and division (/) −

using System;

class Demo {
   static void Main() {
      decimal d1 = 5.8M;
      decimal d2 = 3.2M;
      
      Console.WriteLine("Addition: " + (d1 + d2));
      Console.WriteLine("Subtraction: " + (d1 - d2));
      Console.WriteLine("Multiplication: " + (d1 * d2));
      Console.WriteLine("Division: " + (d1 / d2));
   }
}

The output of the above code is −

Addition: 9.0
Subtraction: 2.6
Multiplication: 18.56
Division: 1.8125

Decimal vs Float vs Double Comparison

Financial Calculation Example

Here's a practical example showing why decimal is preferred for monetary calculations −

using System;

class FinancialCalculation {
   static void Main() {
      decimal price = 19.99M;
      decimal taxRate = 0.08M;
      int quantity = 3;
      
      decimal subtotal = price * quantity;
      decimal tax = subtotal * taxRate;
      decimal total = subtotal + tax;
      
      Console.WriteLine("Price per item: $" + price);
      Console.WriteLine("Quantity: " + quantity);
      Console.WriteLine("Subtotal: $" + subtotal);
      Console.WriteLine("Tax (8%): $" + tax);
      Console.WriteLine("Total: $" + total);
   }
}

The output of the above code is −

Price per item: $19.99
Quantity: 3
Subtotal: $59.97
Tax (8%): $4.7976
Total: $64.7676

Decimal Methods and Conversion

using System;

class DecimalMethods {
   static void Main() {
      decimal value = 123.456789M;
      
      Console.WriteLine("Original: " + value);
      Console.WriteLine("Rounded: " + Math.Round(value, 2));
      Console.WriteLine("Ceiling: " + Math.Ceiling(value));
      Console.WriteLine("Floor: " + Math.Floor(value));
      Console.WriteLine("Truncated: " + Math.Truncate(value));
      
      // Convert to other types
      double doubleVal = (double)value;
      int intVal = (int)value;
      Console.WriteLine("As double: " + doubleVal);
      Console.WriteLine("As int: " + intVal);
   }
}

The output of the above code is −

Original: 123.456789
Rounded: 123.46
Ceiling: 124
Floor: 123
Truncated: 123
As double: 123.456789
As int: 123

Conclusion

The decimal type in C# provides the highest precision for financial calculations with 28-29 significant digits. It requires the M suffix for literals and is essential for applications where exact decimal representation is critical, such as banking and accounting systems.