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C# Math.Abs: Absolute Value

This C# article shows how to use the Math.Abs method. Abs computes absolute numbers.

Math.Abs. An absolute value is not negative.

It is the same as the original value but with no negative sign. The Math.Abs method in the .NET Framework provides a tested absolute value function. It deals with certain edge cases.

Example. It is usually trivial to convert variables to positive values from negative values. The Math.Abs method in the base class library in the .NET Framework provides some error-checking that may be useful.

Tip: The C# compiler does overload resolution based on the parameter type. It infers the appropriate method to use.


Next: This example shows the absolute value of a negative integer, a positive integer, a negative double and a positive double.


C# program that computes absolute values

using System;

class Program
    static void Main()
	// Compute two absolute values.
	int value1 = -1000;
	int value2 = 20;
	int abs1 = Math.Abs(value1);
	int abs2 = Math.Abs(value2);
	// Write integral results.
	// Compute two double absolute values.
	double value3 = -100.123;
	double value4 = 20.20;
	double abs3 = Math.Abs(value3);
	double abs4 = Math.Abs(value4);
	// Write double results.


1000     (Absolute value)
20       (Absolute value)
100.123  (Absolute value)
20.2     (Absolute value)

The C# compiler resolves the four calls to Math.Abs to the System.Math class. It uses the version with an int in its signature for the first two calls, and the version with double for the second two.

Tip: You could cast the variables before passing them as parameters to force the compiler to use a different overload.

Numeric CastsCast to Int

The example program prints eight numbers. Each numeric literal in the source is printed in its initial form and the result of the Math.Abs computation. This means the second version is always positive in the output.


Internals. The Math.Abs method on value types such as int, short and long will use a conditional check that tests if the number if already positive. If the number is positive, it is returned unchanged.

Otherwise, an overflow condition is checked and the unary negation operator is applied, which results in a positive number. If the overflow condition is not useful, you can enhance performance by checking for positive numbers yourself.

For number types such as decimal, double and float, other implementations are called into from Math.Abs, making it a mere wrapper method. For double and float, it is important to use Math.Abs instead of checking for positive yourself.


Tip: The external method invoked is likely much faster and simpler. This is often the case in the .NET Framework.

.NET Framework: C# Methods, Windows and ASP.NET

Discussion. Methods such as Math.Abs must check for already-positive numbers before changing the sign. From the hardware perspective, it is easier to flip the sign bit on a signed integer type. You can apply the unary minus (negation) operator.

Tip: You can take the absolute value of a number that is always negative by simply using the unary negation operator.

Summary. We used Math.Abs for a simple, tested absolute value function that works for signed value types. The Math.Abs method accepts decimal, double, Int16, Int32, Int64 and float types, and all keywords that are aliased to those types.

Also: We noted the implementation of Math.Abs—and some ways you can simplify absolute values in non-general cases.

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