Get absolute value in C#
Get absolute value of argument.
Use Abs() of System.Math class for both of integer and float.
GetAbsoluteValue.cs 
using System;

class GetAbsoluteValue {
    static void Main() {
        // Get absolute value of integer
	Console.WriteLine("Absolute value of  5 is " + System.Math.Abs(5));
	Console.WriteLine("Absolute value of -5 is " + System.Math.Abs(-5));

        // Get absolute value of decimal
	Console.WriteLine("Absolute value of  5.5 is " + System.Math.Abs(5.5));
	Console.WriteLine("Absolute value of -5.5 is " + System.Math.Abs(-5.5));
    }
}
Result 
$ mcs GetAbsoluteValue.cs
$ mono GetAbsoluteValue.exe
Absolute value of  5 is 5
Absolute value of -5 is 5
Absolute value of  5.5 is 5.5
Absolute value of -5.5 is 5.5