C# double

last modified July 5, 2023

In this article we show how to work with double data type in C#.

The double type is one of the fundamental data types in programming. We can define a data type as a set of values, and the allowable operations on those values.

The double is a primitive data type which represents real numbers in computing. The double is an alias for System.Double structure.

Floating point numbers represent real numbers in computing. Real numbers measure continuous quantities, like weight, height, or speed. In C# we have three floating point types: float, double, and decimal.

C# Alias	.NET Type	Size	Precision	Range
float	System.Single	4 bytes	7 digits	+-1.5 x 10^-45 to +-3.4 x 10³⁸
double	System.Double	8 bytes	15-16 digits	+-5.0 x 10^-324 to +-1.7 x 10³⁰⁸
decimal	System.Decimal	16 bytes	28-29 decimal places	+-1.0 x 10^-28 to +-7.9 x 10²⁸

The above table gives the characteristics of the floating point types.

C# double type constants

The double type has some built-in constants.

Program.cs

Console.WriteLine(double.MinValue);
Console.WriteLine(double.MaxValue);

Console.WriteLine(double.E);
Console.WriteLine(double.Pi);
Console.WriteLine(double.Tau);

The program prints five constants.

Console.WriteLine(double.MinValue);
Console.WriteLine(double.MaxValue);

We print the smallest and largest possible value of double type.

Console.WriteLine(double.E);
Console.WriteLine(double.Pi);
Console.WriteLine(double.Tau);

We print three well-known Math constants.

$ dotnet run
-1.7976931348623157E+308
1.7976931348623157E+308
2.718281828459045
3.141592653589793
6.283185307179586

Floating point type suffixes

By default, real numbers are double in C# programs. To use a different type, we must use a suffix. The F/f for float numbers and M/m for decimal numbers.

Program.cs

float n1 = 6.78f;
double n2 = 6.78;
decimal n3 = 6.78m;

Console.WriteLine(n1);
Console.WriteLine(n2);
Console.WriteLine(n3);

Console.WriteLine(n1.GetType());
Console.WriteLine(n2.GetType());
Console.WriteLine(n3.GetType());

In the above program, we use three different literal notations for floating point numbers.

float n1 = 1.234f;

The f suffix is used for a float number.

double n2 = 1.234;

If we do not use a suffix, then it is a double number. We can optionally use the d suffix.

Console.WriteLine(n1.GetType());

The GetType method returns the type of the number.

$ dotnet run
6.78
6.78
6.78
System.Single
System.Double
System.Decimal

C# convert to double

In the next example, we show how to convert values to double type.

Program.cs

float n1 = 6.78f;
decimal n2 = 6.78m;
int n3 = 7;

Console.WriteLine(n1);
Console.WriteLine(n2);
Console.WriteLine(n3);

Console.WriteLine("-------------------");

double d1 = (double) n1;
double d2 = decimal.ToDouble(n2);
double d3 = Convert.ToDouble(n3);

Console.WriteLine(d1);
Console.WriteLine(d2);
Console.WriteLine(d3);

Console.WriteLine("-------------------");

Console.WriteLine(d1.GetType());
Console.WriteLine(d2.GetType());
Console.WriteLine(d3.GetType());

We define three variables having float, decimal, and int types. We convert these values to double type.

float n1 = 6.78f;
decimal n2 = 6.78m;
int n3 = 7;

We define three variables.

double d1 = (double) n1;

We use the casting operation to convert the float value to double.

double d2 = decimal.ToDouble(n2);

In the second case, we convert the decimal to double with decimal.ToDouble built-in method.

double d3 = Convert.ToDouble(n3);

Finally, for the integer type, we utilize the external Convert class.

$ dotnet run
6.78
6.78
7
-------------------
6.78000020980835
6.78
7
-------------------
System.Double
System.Double
System.Double

Note that there is some small error in the first conversion.

C# convert from double type

In the next example we show how to convert from the double type to other data types.

Program.cs

double val = 6.78;

float n1 = (float) val;
decimal n2 = Convert.ToDecimal(val);
int n3  = Convert.ToInt32(val);

Console.WriteLine(n1);
Console.WriteLine(n2);
Console.WriteLine(n3);

Console.WriteLine(n1.GetType());
Console.WriteLine(n2.GetType());
Console.WriteLine(n3.GetType());

We define a single double value. We convert the value to float, decimal, and int.

$ dotnet run
6.78
6.78
7
System.Single
System.Decimal
System.Int32

The double type is inexact

The double type is not exact. There are small rounding errors in calculations. In many cases, these do not pose a problem. For instance, it does not matter if an item is 1.78 mm or 1.7801 mm log.

In financial and currency calculations, these small errors matter. For those types of calculations, we use the decimal type.

Program.cs

double n1 = 0.1 + 0.1 + 0.1;
double n2 = 0.3;

Console.WriteLine(n1);
Console.WriteLine(n2);

if (n1 == n2)
{
    Console.WriteLine("The values are equal");
} else 
{
    Console.WriteLine("The values are not equal");
}

The program demonstrates a small error in a simple calculation with double types.

$ dotnet run
0.30000000000000004
0.3
The values are not equal

The two values are not equal because there is a very small error in the addition operation.

C# round double values

Rounding numbers is adjusting the digits up or down to make calculations easier. We can round

double double.Round(double x, int digits, MidpointRounding mode)

The method rounds a double value to a specified number of fractional digits using the specified rounding mode.

Mode	Description
AwayFromZero	rounded toward the nearest number that's away from zero
ToEven	rounded toward the nearest even number
ToNegativeInfinity	downwards-directed rounding
ToPositiveInfinity	upwards-directed rounding
ToZero	rounding towards zero

The table presents the rounding modes available.

Program.cs

double n1 = 1 / 7d;
double n2 = -1 / 7d;

Console.WriteLine(n1);
Console.WriteLine(n2);

Console.WriteLine("-------------------------");

Console.WriteLine(double.Round(n1, 3, MidpointRounding.ToEven));
Console.WriteLine(double.Round(n2, 3, MidpointRounding.ToEven));

Console.WriteLine("-------------------------");

Console.WriteLine(double.Round(n1, 3, MidpointRounding.AwayFromZero));
Console.WriteLine(double.Round(n2, 3, MidpointRounding.AwayFromZero));

Console.WriteLine("-------------------------");

Console.WriteLine(double.Round(n1, 3, MidpointRounding.ToZero));
Console.WriteLine(double.Round(n2, 3, MidpointRounding.ToZero));

Console.WriteLine("-------------------------");

Console.WriteLine(double.Round(n1, 3, MidpointRounding.ToNegativeInfinity));
Console.WriteLine(double.Round(n2, 3, MidpointRounding.ToNegativeInfinity));

Console.WriteLine("-------------------------");

Console.WriteLine(double.Round(n1, 3, MidpointRounding.ToPositiveInfinity));
Console.WriteLine(double.Round(n2, 3, MidpointRounding.ToPositiveInfinity));

In the example, we have a positive and a negative double value. We round the values using the available rounding modes to three fractional digits.

$ dotnet run 
0.14285714285714285
-0.14285714285714285
-------------------------
0.143
-0.143
-------------------------
0.143
-0.143
-------------------------
0.142
-0.142
-------------------------
0.142
-0.143
-------------------------
0.143
-0.142

Source

Double struct

In this article we worked with double type in C# language.

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My name is Jan Bodnar and I am a passionate programmer with many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.

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C# double

C# double type constants

Floating point type suffixes

C# convert to double

C# convert from double type

The double type is inexact

C# round double values

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