Double.CompareTo Method (Double)
Note 

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Compares this instance to a specified doubleprecision floatingpoint number and returns an integer that indicates whether the value of this instance is less than, equal to, or greater than the value of the specified doubleprecision floatingpoint number.
Assembly: mscorlib (in mscorlib.dll)
Parameters
 value

Type:
System.Double
A doubleprecision floatingpoint number to compare.
Return Value
Type: System.Int32A signed number indicating the relative values of this instance and value.
Return Value  Description 

Less than zero  This instance is less than value. or This instance is not a number (NaN) and value is a number. 
Zero  This instance is equal to value. or Both this instance and value are not a number (NaN), PositiveInfinity, or NegativeInfinity. 
Greater than zero  This instance is greater than value. or This instance is a number and value is not a number (NaN). 
Implements
IComparable<'T>.CompareTo('T)Values must be identical to be considered equal. Particularly when floatingpoint values depend on multiple mathematical operations, it is common for them to lose precision and for their values to be nearly identical except for their least significant digits. Because of this, the return value of the CompareTo method at times may seem surprising. For example, multiplication by a particular value followed by division by the same value should produce the original value. In the following example, however, the computed value turns out to be greater than the original value. Showing all significant digits of the two values by using the "R" standard numeric format string indicates that the computed value differs from the original value in its least significant digits. For information on handling such comparisons, see the Remarks section of the Equals(Double) method.
This method implements the System.IComparable<'T> interface and performs slightly better than the Double.CompareTo method because it does not have to convert the value parameter to an object.
Note that, although an object whose value is NaN is not considered equal to another object whose value is NaN (even itself), the IComparable<'T> interface requires that A.CompareTo(A) return zero.
Depending on your programming language, it might be possible to code a CompareTo method where the parameter type has fewer bits (is narrower) than the instance type. This is possible because some programming languages perform an implicit widening conversion that represents the parameter as a type with as many bits as the instance.
For example, suppose the instance type is Double and the parameter type is Int32. The Microsoft C# compiler generates instructions to represent the value of the parameter as a Double object, then generates a Double.CompareTo(Double) method that compares the values of the instance and the widened representation of the parameter.
Consult your programming language's documentation to determine if its compiler performs implicit widening conversions of numeric types. For more information, see the Type Conversion Tables in the .NET Framework topic.
The precision of floatingpoint numbers beyond the documented precision is specific to the implementation and version of the .NET Framework. Consequently, a comparison of two particular numbers might change between versions of the .NET Framework because the precision of the numbers' internal representation might change.
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1