简单、干净、快捷

private static string GetOrdinalSuffix(int num)
{
    string number = num.ToString();
    if (number.EndsWith("11")) return "th";
    if (number.EndsWith("12")) return "th";
    if (number.EndsWith("13")) return "th";
    if (number.EndsWith("1")) return "st";
    if (number.EndsWith("2")) return "nd";
    if (number.EndsWith("3")) return "rd";
    return "th";
}

或者更好的是，作为一个扩展方法

public static class IntegerExtensions
{
    public static string DisplayWithSuffix(this int num)
    {
        string number = num.ToString();
        if (number.EndsWith("11")) return number + "th";
        if (number.EndsWith("12")) return number + "th";
        if (number.EndsWith("13")) return number + "th";
        if (number.EndsWith("1")) return number + "st";
        if (number.EndsWith("2")) return number + "nd";
        if (number.EndsWith("3")) return number + "rd";
        return number + "th";
    }
}

现在你可以打电话了

int a = 1;
a.DisplayWithSuffix(); 

甚至直接到

1.DisplayWithSuffix();

private static string GetOrd(int num) => $"{num}{(!(Range(11, 3).Any(n => n == num % 100) ^ Range(1, 3).All(n => n != num % 10)) ? new[] { "ˢᵗ", "ⁿᵈ", "ʳᵈ" }[num % 10 - 1] : "ᵗʰ")}";

如果有人在找一句俏皮话。

编辑:正如YM_Industries在评论中指出的那样，samjudson的答案确实适用于超过1000的数字，nickf的评论似乎已经消失了，我不记得我看到的问题是什么。留下这个答案在这里比较时间。

正如nickf在评论中指出的(编辑:现在丢失了)，很多数字> 999都不起作用。

以下是一个基于samjudson的公认答案的修改版本。

public static String GetOrdinal(int i)
{
    String res = "";

    if (i > 0)
    {
        int j = (i - ((i / 100) * 100));

        if ((j == 11) || (j == 12) || (j == 13))
            res = "th";
        else
        {
            int k = i % 10;

            if (k == 1)
                res = "st";
            else if (k == 2)
                res = "nd";
            else if (k == 3)
                res = "rd";
            else
                res = "th";
        }
    }

    return i.ToString() + res;
}

同样，Shahzad Qureshi使用字符串操作的回答也很好，但它确实有性能损失。为了生成大量这样的类型，LINQPad示例程序使字符串版本比整数版本慢6-7倍(尽管您必须生成很多才会注意到)。

LINQPad例子:

void Main()
{
    "Examples:".Dump();

    foreach(int i in new int[] {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 22, 113, 122, 201, 202, 211, 212, 2013, 1000003, 10000013 })
        Stuff.GetOrdinal(i).Dump();

    String s;

    System.Diagnostics.Stopwatch sw = System.Diagnostics.Stopwatch.StartNew();

    for(int iter = 0; iter < 100000; iter++)
        foreach(int i in new int[] {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 22, 113, 122, 201, 202, 211, 212, 2013, 1000003, 1000013 })
            s = Stuff.GetOrdinal(i);

    "Integer manipulation".Dump();
    sw.Elapsed.Dump();

    sw.Restart();

    for(int iter = 0; iter < 100000; iter++)
        foreach(int i in new int[] {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 22, 113, 122, 201, 202, 211, 212, 2013, 1000003, 1000013 })
            s = (i.ToString() + Stuff.GetOrdinalSuffix(i));

    "String manipulation".Dump();
    sw.Elapsed.Dump();
}

public class Stuff
{
        // Use integer manipulation
        public static String GetOrdinal(int i)
        {
                String res = "";

                if (i > 0)
                {
                        int j = (i - ((i / 100) * 100));

                        if ((j == 11) || (j == 12) || (j == 13))
                                res = "th";
                        else
                        {
                                int k = i % 10;

                                if (k == 1)
                                        res = "st";
                                else if (k == 2)
                                        res = "nd";
                                else if (k == 3)
                                        res = "rd";
                                else
                                        res = "th";
                        }
                }

                return i.ToString() + res;
        }

        // Use string manipulation
        public static string GetOrdinalSuffix(int num)
        {
                if (num.ToString().EndsWith("11")) return "th";
                if (num.ToString().EndsWith("12")) return "th";
                if (num.ToString().EndsWith("13")) return "th";
                if (num.ToString().EndsWith("1")) return "st";
                if (num.ToString().EndsWith("2")) return "nd";
                if (num.ToString().EndsWith("3")) return "rd";
                return "th";
        }
}

FWIW，对于MS-SQL，这个表达式将完成工作。将第一个WHEN (WHEN num % 100 IN (11,12,13) THEN 'th')作为列表中的第一个，因为这依赖于在其他尝试之前尝试。

CASE
  WHEN num % 100 IN (11, 12, 13) THEN 'th' -- must be tried first
  WHEN num % 10 = 1 THEN 'st'
  WHEN num % 10 = 2 THEN 'nd'
  WHEN num % 10 = 3 THEN 'rd'
  ELSE 'th'
END AS Ordinal

对于Excel:

=MID("thstndrdth",MIN(9,2*RIGHT(A1)*(MOD(A1-11,100)>2)+1),2)

表达式(MOD(A1- 11100)>2)对于除以11,12,13结尾的任何数字(FALSE = 0)外的所有数字都是TRUE(1)。因此2 * RIGHT(A1) * (MOD(A1- 11100)>2) +1)对于11/12/13最终为1，否则: 1等于3 2点到5点， 3至7点 其他:9 -所需的2个字符从该位置开始的“第thstndrdth”中选择。

如果你真的想把它直接转换成SQL，这对我来说适用于一些测试值:

DECLARE @n as int
SET @n=13
SELECT SubString(  'thstndrdth'
                 , (SELECT MIN(value) FROM
                     (SELECT 9 as value UNION
                      SELECT 1+ (2* (ABS(@n) % 10)  *  CASE WHEN ((ABS(@n)+89) % 100)>2 THEN 1 ELSE 0 END)
                     ) AS Mins
                   )
                 , 2
                )

public static string OrdinalSuffix(int ordinal)
{
    //Because negatives won't work with modular division as expected:
    var abs = Math.Abs(ordinal); 

    var lastdigit = abs % 10; 

    return 
        //Catch 60% of cases (to infinity) in the first conditional:
        lastdigit > 3 || lastdigit == 0 || (abs % 100) - lastdigit == 10 ? "th" 
            : lastdigit == 1 ? "st" 
            : lastdigit == 2 ? "nd" 
            : "rd";
}

这是dart中的实现，可以根据语言进行修改。

String getOrdinalSuffix(int num){
    if (num.toString().endsWith("11")) return "th";
    if (num.toString().endsWith("12")) return "th";
    if (num.toString().endsWith("13")) return "th";
    if (num.toString().endsWith("1")) return "st";
    if (num.toString().endsWith("2")) return "nd";
    if (num.toString().endsWith("3")) return "rd";
    return "th";
}