From e7f23316633e926afa825596d258e1ccca00b607 Mon Sep 17 00:00:00 2001
From: Robby Findler <robby@racket-lang.org>
Date: Mon, 15 Jun 2020 15:01:18 -0500
Subject: [PATCH] correct n->th

closes #3238
---
 .../tests/racket/contract/helpers.rkt         | 37 +++++++++++++++++++
 .../collects/racket/contract/private/guts.rkt | 13 ++++---
 2 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/pkgs/racket-test/tests/racket/contract/helpers.rkt b/pkgs/racket-test/tests/racket/contract/helpers.rkt
index 7e1a234c97..e2a5edd493 100644
--- a/pkgs/racket-test/tests/racket/contract/helpers.rkt
+++ b/pkgs/racket-test/tests/racket/contract/helpers.rkt
@@ -125,3 +125,40 @@
 (check-equal? (f 1 0 3 4) (list 1 0 3 4))
 (check-equal? (f 0 2 3 4) (list 0 2 3 4))
 (check-equal? (f 0 2 3 4) (list 0 2 3 4))
+
+(check-equal? (n->th 0) "0th")
+(check-equal? (n->th 1) "1st")
+(check-equal? (n->th 2) "2nd")
+(check-equal? (n->th 3) "3rd")
+(check-equal? (n->th 4) "4th")
+(check-equal? (n->th 5) "5th")
+(check-equal? (n->th 10) "10th")
+(check-equal? (n->th 11) "11th")
+(check-equal? (n->th 12) "12th")
+(check-equal? (n->th 13) "13th")
+(check-equal? (n->th 14) "14th")
+(check-equal? (n->th 15) "15th")
+(check-equal? (n->th 20) "20th")
+(check-equal? (n->th 21) "21st")
+(check-equal? (n->th 22) "22nd")
+(check-equal? (n->th 23) "23rd")
+(check-equal? (n->th 24) "24th")
+(check-equal? (n->th 25) "25th")
+(check-equal? (n->th 100) "100th")
+(check-equal? (n->th 101) "101st")
+(check-equal? (n->th 102) "102nd")
+(check-equal? (n->th 103) "103rd")
+(check-equal? (n->th 104) "104th")
+(check-equal? (n->th 105) "105th")
+(check-equal? (n->th 110) "110th")
+(check-equal? (n->th 111) "111th")
+(check-equal? (n->th 112) "112th")
+(check-equal? (n->th 113) "113th")
+(check-equal? (n->th 114) "114th")
+(check-equal? (n->th 115) "115th")
+(check-equal? (n->th 120) "120th")
+(check-equal? (n->th 121) "121st")
+(check-equal? (n->th 122) "122nd")
+(check-equal? (n->th 123) "123rd")
+(check-equal? (n->th 124) "124th")
+(check-equal? (n->th 125) "125th")
diff --git a/racket/collects/racket/contract/private/guts.rkt b/racket/collects/racket/contract/private/guts.rkt
index 892a55e0a7..b1030a277d 100644
--- a/racket/collects/racket/contract/private/guts.rkt
+++ b/racket/collects/racket/contract/private/guts.rkt
@@ -961,11 +961,14 @@
 (define (n->th n)
   (string-append 
    (number->string n)
-   (case (modulo n 10)
-     [(1) "st"]
-     [(2) "nd"]
-     [(3) "rd"]
-     [else "th"])))
+   (case (remainder n 100)
+     [(11 12 13) "th"]
+     [else
+      (case (modulo n 10)
+        [(1) "st"]
+        [(2) "nd"]
+        [(3) "rd"]
+        [else "th"])])))
 
 (define (nth-element-of/alloc n)
   (format "the ~a element of" (n->th n)))