From 4d628f1e0675144dddb903665fd94040fa49b832 Mon Sep 17 00:00:00 2001
From: Abigail <abigail@abigail.be>
Date: Mon, 25 Jan 2021 19:21:08 +0100
Subject: C solution for week 2, part 2

---
 challenge-002/abigail/README.md |   1 +
 challenge-002/abigail/c/ch-2.c  | 106 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 107 insertions(+)
 create mode 100644 challenge-002/abigail/c/ch-2.c

diff --git a/challenge-002/abigail/README.md b/challenge-002/abigail/README.md
index 4642bfbfa6..bb5cb18c8f 100644
--- a/challenge-002/abigail/README.md
+++ b/challenge-002/abigail/README.md
@@ -37,6 +37,7 @@ one number per line. Programs will use an option, -t (to base 35), or
 
 ### Solutions
 * [AWK](awk/ch-2.awk)
+* [C](c/ch-2.c)
 * [Lua](lua/ch-2.lua)
 * [Node](node/ch-2.js)
 * [Perl](perl/ch-2.pl)
diff --git a/challenge-002/abigail/c/ch-2.c b/challenge-002/abigail/c/ch-2.c
new file mode 100644
index 0000000000..20cdd146d6
--- /dev/null
+++ b/challenge-002/abigail/c/ch-2.c
@@ -0,0 +1,106 @@
+# include <stdlib.h>
+# include <stdio.h>
+# include <string.h>
+# include <unistd.h>
+
+/*
+ * See ../README.md
+ */
+
+/*
+ * Run as: cc -o ch-2.o ch-2.c; ./ch-2.o {-f | -t} < input-file
+ *
+ *    -f: Translate from base 35 to base 10
+ *    -t: Translate to base 35 from base 35
+ */
+
+int BASE = 35;
+
+/*
+ * Convert from base 35 to base 10
+ */
+long long from_base (char * number) {
+    long long out = 0;
+    while (* number) {
+        char ch = * number ++;
+        int  n  = ch <= '9' ? ch - '0' : ch - 'A' + 10;
+        out    *= BASE;
+        out    += n;
+    }
+    return (out);
+}
+
+/*
+ * Convert to base 35 from base 10
+ */
+char * to_base (long long number) {
+    char * out;
+    if ((out = (char *) malloc (64 * sizeof (char))) == NULL) {
+        fprintf (stderr, "Out of memory\n");
+        exit (1);
+    }
+    size_t i = 0;
+    while (number > 0) {
+        int rest = number % BASE;
+        out [i ++] = rest < 10 ? '0' + rest
+                               : 'A' + rest - 10;
+        number = number / BASE;
+    }
+    out [i] = '\0';
+
+    /*
+     * Reverse the string
+     */
+    for (size_t j = 0; 2 * j < i; j ++) {
+        char t          = out [j];
+        out [j]         = out [i - j - 1];
+        out [i - j - 1] = t;
+    }
+
+    return (out);
+}
+
+int main (int argc, char ** argv) {
+    char *  line    = NULL;
+    size_t  len     = 0;
+    size_t  strlen;
+
+    int do_to_base   = 0;
+    int do_from_base = 0;
+    char ch;
+
+    /*
+     * Parse and validate options
+     */
+    while ((ch = getopt (argc, argv, "tf")) != -1) {
+        switch (ch) {
+            case 't':
+                do_to_base = 1;
+                break;
+            case 'f':
+                do_from_base = 1;
+                break;
+        }
+    }
+
+    if (do_to_base + do_from_base != 1) {
+        fprintf (stderr, "Need exactly one of -f or -t options\n");
+        exit (1);
+    }
+
+    while ((strlen = getline (&line, &len, stdin)) != -1) {
+        line [strlen - 1] = '\0'; /* Chop off newline */
+        if (do_from_base) {
+            printf ("%lld\n", from_base (line));
+        }
+        if (do_to_base) {
+            char * out = to_base (atoll (line));
+            printf ("%s\n", out);
+            free (out);
+        }
+        char * line_ptr = line;
+    }
+    free (line);
+
+    return (0);
+}
-- 
cgit