C# / .NET - Math.Floor() method example

The Math.Floor() function returns an integer value that is smaller than or equal to the argument - the result of round down operation.  

using System;

public class Program
{
    public static void Main(string[] args) 
    {
        Console.WriteLine( Math.Floor(  5.0  )); //  5
 
        Console.WriteLine( Math.Floor(  2.49 )); //  2
        Console.WriteLine( Math.Floor(  2.50 )); //  2
        Console.WriteLine( Math.Floor(  2.51 )); //  2
 
        Console.WriteLine( Math.Floor( -2.49 )); // -3
        Console.WriteLine( Math.Floor( -2.50 )); // -3
        Console.WriteLine( Math.Floor( -2.51 )); // -3
 
        Console.WriteLine( Math.Floor(  0.999 )); //  0
        Console.WriteLine( Math.Floor(  1.001 )); //  1
        Console.WriteLine( Math.Floor( -1.001 )); // -2
    }
}

1. Documentation

namespace System
{
    public static class Math
    {
        // ...
        public static decimal Floor(decimal number) { ... }
        public static double Floor(double number) { ... }
        // ...
    }
}

2. Rounding with precision down-to n places example

using System;

public class Program
{
    static double FloorPrecised(double number, int precision)
    {
        double power = Math.Pow(10, precision);

        return Math.Floor(number * power) / power;
    }

    public static void Main(string[] args) 
    {
        Console.WriteLine( FloorPrecised(     5  ,  0 ) ); // 5
        Console.WriteLine( FloorPrecised(    5.0 ,  0 ) ); // 5
        Console.WriteLine( FloorPrecised(      .5,  0 ) ); // 0

        Console.WriteLine( FloorPrecised(  1.1234,  0 ) ); // 1
        Console.WriteLine( FloorPrecised(  1.1234,  1 ) ); // 1.1
        Console.WriteLine( FloorPrecised(  1.1235,  2 ) ); // 1.12
        Console.WriteLine( FloorPrecised(  1.1235,  3 ) ); // 1.123

        Console.WriteLine( FloorPrecised( -1.1234,  0 ) ); // -2
        Console.WriteLine( FloorPrecised( -1.1234,  1 ) ); // -1.2
        Console.WriteLine( FloorPrecised( -1.1234,  2 ) ); // -1.13
        Console.WriteLine( FloorPrecised( -1.1234,  3 ) ); // -1.124

        Console.WriteLine( FloorPrecised(    1234, -1 ) ); // 1230
        Console.WriteLine( FloorPrecised(    1234, -2 ) ); // 1200
        Console.WriteLine( FloorPrecised(    1234, -3 ) ); // 1000

        Console.WriteLine( FloorPrecised(  5_000.000_001,  0 ) ); // 5000
        Console.WriteLine( FloorPrecised(  5_000.000_001,  6 ) ); // 5000.000001
        Console.WriteLine( FloorPrecised(  5_000.000_001, -3 ) ); // 5000
    }
}

References

1. Floor and ceiling functions - Wikipedia