How do I provide a suffix for days of the month?

Question

I need a function to return a suffix for days when displaying text like the "th" in "Wednesday June 5th, 2008".

It only need work for the numbers 1 through 31 (no error checking required) and English.

Answer 1

The following function works for C:

char *makeDaySuffix (int day) {
    switch (day) {
        case 1: case 21: case 31: return "st";
        case 2: case 22:          return "nd";
        case 3: case 23:          return "rd";
    }
    return "th";
}

As requested, it only works for the numbers 1 through 31 inclusive. If you want (possibly, but not necessarily) raw speed, you could try:

char *makeDaySuffix (int day) {
    static const char * const suffix[] = {
        "",
        "st","nd","rd","th","th","th","th","th","th","th",
        "th","th","th","th","th","th","th","th","th","th"
        "st","nd","rd","th","th","th","th","th","th","th"
        "st"
    };
    return suffix[day];
}

Just keep in mind that, with the compilers of today, naive assumptions about what is faster in a high-level language may not be correct: measure, don't guess.

Answer 2

Please see this question.

Answer 3

Here is an alternative which should work for larger numbers too:

static const char *daySuffixLookup[] = { "th","st","nd","rd","th",
                           "th","th","th","th","th" };

const char *daySuffix(int n)
{
    if(n % 100 >= 11 && n % 100 <= 13)
        return "th";

    return daySuffixLookup[n % 10];
}

Answer 4

const char *getDaySuffix(int day) {
    if (day%100 > 10 && day%100 < 14)
        return "th";
    switch (day%10) {
        case 1:  return "st";
        case 2:  return "nd";
        case 3:  return "rd";
        default: return "th";
    };
}

This one works for any number, not just 1-31.

Answer 5

See my question here: http://stackoverflow.com/questions/135946/i18n-able-way-to-get-number-ordinal-in-cmfc-on-windows-1-1st-2-2nd-etc (it's not the C# one).

Summary: looks like there's no way yet, with your limited requirements you can just use a simple function like the one posted.