The rules are as follows:
- st is used with numbers ending in 1 (e.g. 1st, pronounced first)
- nd is used with numbers ending in 2 (e.g. 92nd, pronounced ninety-second)
- rd is used with numbers ending in 3 (e.g. 33rd, pronounced thirty-third)
- As an exception to the above rules, all the "teen" numbers ending with 11, 12 or 13 use -th (e.g. 11th, pronounced eleventh, 112th, pronounced one hundred [and] twelfth)
- th is used for all other numbers (e.g. 9th, pronounced ninth).
The following JavaScript code (rewritten in Jun '14) accomplishes this:
function ordinal_suffix_of(i) {
var j = i % 10,
k = i % 100;
if (j == 1 && k != 11) {
return i + "st";
}
if (j == 2 && k != 12) {
return i + "nd";
}
if (j == 3 && k != 13) {
return i + "rd";
}
return i + "th";
}
Sample output for numbers between 0-115:
0 0th
1 1st
2 2nd
3 3rd
4 4th
5 5th
6 6th
7 7th
8 8th
9 9th
10 10th
11 11th
12 12th
13 13th
14 14th
15 15th
16 16th
17 17th
18 18th
19 19th
20 20th
21 21st
22 22nd
23 23rd
24 24th
25 25th
26 26th
27 27th
28 28th
29 29th
30 30th
31 31st
32 32nd
33 33rd
34 34th
35 35th
36 36th
37 37th
38 38th
39 39th
40 40th
41 41st
42 42nd
43 43rd
44 44th
45 45th
46 46th
47 47th
48 48th
49 49th
50 50th
51 51st
52 52nd
53 53rd
54 54th
55 55th
56 56th
57 57th
58 58th
59 59th
60 60th
61 61st
62 62nd
63 63rd
64 64th
65 65th
66 66th
67 67th
68 68th
69 69th
70 70th
71 71st
72 72nd
73 73rd
74 74th
75 75th
76 76th
77 77th
78 78th
79 79th
80 80th
81 81st
82 82nd
83 83rd
84 84th
85 85th
86 86th
87 87th
88 88th
89 89th
90 90th
91 91st
92 92nd
93 93rd
94 94th
95 95th
96 96th
97 97th
98 98th
99 99th
100 100th
101 101st
102 102nd
103 103rd
104 104th
105 105th
106 106th
107 107th
108 108th
109 109th
110 110th
111 111th
112 112th
113 113th
114 114th
115 115th