C# Convert Miles to Kilometers

Convert miles, kilometers. A figure in miles can be converted to kilometers.

The United States has standardized on miles. Most other countries use the superior metric system. It is important to maintain compatibility with many cultures.

Required input and output for distance conversion

Input:  200 m
	321.9 km
	500 km
	310.7 m

Output: 321.9 km
	200 m
	310.7 m
	500 km

Example. Here we look at some useful conversion methods for this problem. The solution consists of one static class and two methods in it. These methods are effective in converting from miles to kilometers and back again.

Static Method

C# program that converts miles and kilometers

using System;

class Program
{
    static void Main()
    {
	//
	// Convert miles to kilometers.
	//
	double miles1 = 200;
	double kilometers1 = ConvertDistance.ConvertMilesToKilometers(200);
	Console.WriteLine("{0} = {1}", miles1, kilometers1);

	//
	// Convert kilometers to miles.
	//
	double kilometers2 = 321.9;
	double miles2 = ConvertDistance.ConvertKilometersToMiles(321.9);
	Console.WriteLine("{0} = {1}", kilometers2, miles2);

	//
	// Convert kilometers to miles (again).
	//
	double kilometers3 = 500;
	double miles3 = ConvertDistance.ConvertKilometersToMiles(500);
	Console.WriteLine("{0} = {1}", kilometers3, miles3);

	//
	// Convert miles to kilometers (again).
	//
	double miles4 = 310.7;
	double kilometers4 = ConvertDistance.ConvertMilesToKilometers(310.7);
	Console.WriteLine("{0} = {1}", miles4, kilometers4);
    }
}

public static class ConvertDistance
{
    public static double ConvertMilesToKilometers(double miles)
    {
	//
	// Multiply by this constant and return the result.
	//
	return miles * 1.609344;
    }

    public static double ConvertKilometersToMiles(double kilometers)
    {
	//
	// Multiply by this constant.
	//
	return kilometers * 0.621371192;
    }
}

Output

200 = 321.8688
321.9 = 200.0193867048
500 = 310.685596
310.7 = 500.0231808

Double stores numbers that are larger and have decimal places. It consumes more memory and is slower to process. The doubles here are float64 types, meaning they are twice as large as an int.

Double

Constants used. Each method above uses a constant for the conversion. For regular stuff, these are fine. The compiler will treat these constants internally as float64 values. These are in a static class, which doesn't store state.

Tip: Static classes are just a syntactic feature of the C# language, but they help clarify the code.

Discussion. As I noted, the double type here is actually termed float64, meaning a 64-bit number. This snippet shows the ConvertKilometersToMiles method. You can see it uses the mul opcode to multiply.

Info: The ldrc.r8 opcode pushes the supplied value (the 0.621371192) onto the stack as a float.

Method implementation: IL

.method public hidebysig static float64 ConvertKilometersToMiles(float64 k)
    cil managed
{
    .maxstack 8
    L_0000: ldarg.0
    L_0001: ldc.r8 0.621371192
    L_000a: mul
    L_000b: ret
}

Summary. Figures in miles can be converted to km. It is interesting the extent of the loss of precision. In chemistry, there is a concept of significant digits, and that concept certainly applies here as well.

Review: We saw how the methods are converted into MSIL. We also used a static class to logically store static methods.

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