How Can I Efficiently Create Ordinal Numbers (e.g., 1st, 2nd, 3rd) in C#?

Creating ordinal numbers in C#: a convenient way

Representing numbers as ordinal numbers (e.g., 1st, 2nd, 3rd, etc.) can be a programming challenge in C#.

String.Format() can be implemented?

Unfortunately, String.Format() does not directly support ordinal formatting.

Solution: Create a custom function

To generate ordinal numbers efficiently, you can create a custom function:

<code class="language-csharp">public static string AddOrdinal(int num)
{
    if (num <= 0) return num.ToString(); //处理0及负数

    string number = num.ToString();
    int lastDigit = num % 10;
    int lastTwoDigits = num % 100;

    if (lastTwoDigits >= 11 && lastTwoDigits <= 13)
    {
        return number + "th";
    }
    else if (lastDigit == 1)
    {
        return number + "st";
    }
    else if (lastDigit == 2)
    {
        return number + "nd";
    }
    else if (lastDigit == 3)
    {
        return number + "rd";
    }
    else
    {
        return number + "th";
    }
}</code>

Example usage:

<code class="language-csharp">Console.WriteLine(AddOrdinal(1));  // 输出 "1st"
Console.WriteLine(AddOrdinal(2));  // 输出 "2nd"
Console.WriteLine(AddOrdinal(3));  // 输出 "3rd"
Console.WriteLine(AddOrdinal(12)); // 输出 "12th"
Console.WriteLine(AddOrdinal(21)); // 输出 "21st"
Console.WriteLine(AddOrdinal(0));  // 输出 "0"
Console.WriteLine(AddOrdinal(-5)); // 输出 "-5"</code>

Internationalization instructions:

This method is for English ordinal numbers. For internationalization, consider researching the specific ordinal formats for each language and adapting the function accordingly.

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