在 c # 中是否有任何算法来使一个单词单复数化？

Most ORMs have a stab at it, although they generally aren't perfect. I know Castle has it's Inflector Class you can probably poke around. Doing it "perfectly" isn't an easy task though (English "rules" aren't really rules :)), so it depends if you are happy with a "reasonable guess" approach.

I can do it for Esperanto, with no special cases!

string plural(string noun) { return noun + "j"; }

For English, it would be useful to become familiar with the rules for Regular Plurals of Nouns, as well as Irregular Plurals of Nouns. There is a whole Wikipedia article on the English plural, which may have some helpful information too.

I cheated in Java - I wanted to be able to produce a correct string for "There were n something(s)", so I wrote the foll. little overloaded utility method:

static public String pluralize(int val, String sng) {
return pluralize(val,sng,(sng+"s"));
}


static public String pluralize(int val, String sng, String plu) {
return (val+" "+(val==1 ? sng : plu));
}

invoked like so

System.out.println("There were "+pluralize(count,"something"));
System.out.println("You have broken "+pluralize(count,"knife","knives"));

Subsonic 3 has an Inflector class which impressed me by turning Person into People. I peeked at the source and found it naturally cheats a little with a hardcoded list but that's really the only way of doing it in English and how humans do it - we remember the singular and plural of each word and don't just apply a rule. As there's not masculine/feminine(/neutral) to add to the mix it's a lot simpler.

Here's a snippet:

AddSingularRule("^(ox)en", "$1");
AddSingularRule("(vert|ind)ices$", "$1ex");
AddSingularRule("(matr)ices$", "$1ix");
AddSingularRule("(quiz)zes$", "$1");


AddIrregularRule("person", "people");
AddIrregularRule("man", "men");
AddIrregularRule("child", "children");
AddIrregularRule("sex", "sexes");
AddIrregularRule("tax", "taxes");
AddIrregularRule("move", "moves");


AddUnknownCountRule("equipment");

It accounts for some words not having plural equivalents, like the equipment example. As you can probably tell it does a simple Regex replace using $1.

Update:
It appears Subsonic's Inflector is infact the Castle ActiveRecord Inflector class!

I whipped one together based on the Rails pluralizer. You can see my blog post here, or on github here

output = Formatting.Pluralization(100, "sausage");

You also have the System.Data.Entity.Design.PluralizationServices.PluralizationService.

UPDATE: Old answer deserves update. There's now also Humanizer: https://github.com/MehdiK/Humanizer

I've created a tiny library for this in .net (C#), called Pluralizer (unsurprisingly).

It's meant to work with full sentences, something like String.Format does.

It basically works like this:

var target = new Pluralizer();
var str = "There {is} {_} {person}.";


var single = target.Pluralize(str, 1);
Assert.AreEqual("There is 1 person.", single);


// Or use the singleton if you're feeling dirty:
var several = Pluralizer.Instance.Pluralize(str, 47);
Assert.AreEqual("There are 47 people.", several);

It can also do way more than that. Read more about it on my blog. It's also available in NuGet.

As the question was for C#, here is a nice variation on Software Monkey's solution (again a bit of a "cheat", but for me really the most practical and reusable way of doing this):

    public static string Pluralize(this string singularForm, int howMany)
{
return singularForm.Pluralize(howMany, singularForm + "s");
}


public static string Pluralize(this string singularForm, int howMany, string pluralForm)
{
return howMany == 1 ? singularForm : pluralForm;
}

The usage is as follows:

"Item".Pluralize(1) = "Item"
"Item".Pluralize(2) = "Items"


"Person".Pluralize(1, "People") = "Person"
"Person".Pluralize(2, "People") = "People"

You can use PluralizationService of System.Data.Entity (.NET Framework 4.0), as shown in this page: http://zquanghoangz.blogspot.it/2012/02/beginner-with-pluralizationservices.html

Not much documentation from MSDN on the specific usage of the PluralizationService class so here is a unit test class (NUnit) to show basic usage. Notice the odd test case at the bottom that shows the service isn't perfect when it comes to non-standard plural forms.

[TestFixture]
public class PluralizationServiceTests
{
[Test]
public void Test01()
{
var service = PluralizationService.CreateService(CultureInfo.CurrentCulture);


Assert.AreEqual("tigers", service.Pluralize("tiger"));
Assert.AreEqual("processes", service.Pluralize("process"));
Assert.AreEqual("fungi", service.Pluralize("fungus"));


Assert.AreNotEqual("syllabi", service.Pluralize("syllabus")); // wrong pluralization
}
}

Using Microsoft's Northwind example database:

 System.Data.Entity.Design.PluralizationServices.PluralizationService.CreateService(new System.Globalization.CultureInfo("en-US"));

Singularize does not Singularize "Order_Details" It returns "Order_Details" with the s at the end. What is the work around?