Decimal Types in C# (Float, Double, and Decimal)

Decimal numbers allow us to represent real numbers, that is, those that can have a fractional part and be positive or negative.

In C#, the main types for storing decimal numbers are float, double, and decimal.

Each has a specific range and precision, which must be considered depending on the type of calculations to be performed.

Floating Point: float and double

The float and double types are Binary Floating-Point types. They are designed following the IEEE 754 standard, which is the norm followed by almost all modern processors for fast mathematics.

Internally, they do not store the exact number. They store a scientific approximation based on three parts:

This allows representing astronomically large or microscopically small numbers, but at a cost: loss of precision.

float gravity = 9.81f; // Note the 'f' at the end

double sunDistance = 149_600_000.5; // By default it's double

double electronMass = 9.10938356e-31; // 9.109... x 10^-31
float lightSpeed = 2.998e8f;        // Approximately 300,000 km/s

double x = 0.0 / 0.0;
if (double.IsNaN(x))
{
    Console.WriteLine("The result is NaN");
}

double a = 0.1;
double b = 0.2;
double sum = a + b;

Console.WriteLine(sum == 0.3); // True?

The High-Precision Solution decimal

If float and double are fast but “imprecise”, decimal is the complete opposite.

The decimal type is a 128-bit Floating-Point type specifically designed for financial and monetary calculations. Unlike its siblings, decimal uses base 10 instead of base 2 for its fractional part.

This means numbers like are represented exactly.

decimal price = 19.99m; // The 'm' is MANDATORY
decimal tax = 0.21m;
decimal total = price * (1 + tax); // Exact calculation, without strange rounding errors

If you try to assign a double literal to a decimal without the m suffix, the compiler will give you an error. C# protects you from losing precision unintentionally.

Common Mathematical Operations

Arithmetic operations are similar to those for integers. We can perform addition, subtraction, multiplication, and division with floating-point numbers.

double x = 10.5;
double y = 3.2;

double sum = x + y;
double subtraction = x - y;
double multiplication = x * y;
double division = x / y;

Console.WriteLine($"Sum: {sum}");
Console.WriteLine($"Subtraction: {subtraction}");
Console.WriteLine($"Multiplication: {multiplication}");
Console.WriteLine($"Division: {division}");

Practical Examples

decimal principal = 1000.0m; // Initial capital
decimal interestRate = 0.05m; // Annual interest rate (5%)
int years = 10;               // Period in years

decimal finalAmount = principal * (decimal)Math.Pow((double)(1 + interestRate), years);
Console.WriteLine($"Final amount after {years} years: {finalAmount:C}");

double celsius = 25.0;
double fahrenheit = (celsius * 9 / 5) + 32;
Console.WriteLine($"{celsius}°C is equal to {fahrenheit}°F");

using System;
using System.Linq;

public class Statistics
{
    public static void Main()
    {
        double[] values = { 1.5, 2.3, 3.1, 4.7, 5.8 };

        double mean = values.Average();
        double sumOfSquares = values.Select(val => Math.Pow(val - mean, 2)).Sum();
        double standardDeviation = Math.Sqrt(sumOfSquares / values.Length);

        Console.WriteLine($"Mean: {mean}");
        Console.WriteLine($"Standard Deviation: {standardDeviation}");
    }
}