diff --git a/2019/RESULTS.txt b/2019/RESULTS.txt
index 119045e..8ec6845 100644
--- a/2019/RESULTS.txt
+++ b/2019/RESULTS.txt
@@ -39,3 +39,17 @@ aoc-c : res=860
 aoc-c : res=9238
 	time: 0:00.00 real, 0.00 user, 0.00 sys
 	context-switch:	0+1, page-faults: 0+98
+
+=========================================
+================= day04 =================
+=========================================
+
++++++++++++++++++ part 1
+aoc-c : res=2090
+	time: 0:00.01 real, 0.01 user, 0.00 sys
+	context-switch:	2+1, page-faults: 0+88
+
++++++++++++++++++ part 2
+aoc-c : res=1419
+	time: 0:00.01 real, 0.00 user, 0.00 sys
+	context-switch:	3+1, page-faults: 0+91
diff --git a/2019/day03/aoc-c.c b/2019/day03/aoc-c.c
index 7d51f68..fc84ab2 100644
--- a/2019/day03/aoc-c.c
+++ b/2019/day03/aoc-c.c
@@ -56,7 +56,8 @@ static struct list_head *parse(struct list_head *wires)
         int totdist = 0;
 
         if ((buflen = getline(&buf, &alloc, stdin)) <= 0) {
-            fprintf(stderr, "error %d reading file.\n", errno);
+            fprintf(stderr, "error %d reading input.\n", errno);
+            wires = NULL;
             goto end;
         }
 
diff --git a/2019/day04/README.org b/2019/day04/README.org
index 0d91e7a..18ae1ae 100644
--- a/2019/day04/README.org
+++ b/2019/day04/README.org
@@ -21,4 +21,23 @@ Other than the range rule, the following are true:
 /How many different passwords/ within the range given in your puzzle
 input meet these criteria?
 
-Your puzzle input is =130254-678275=.
+Your puzzle answer was =2090=.
+
+** --- Part Two ---
+An Elf just remembered one more important detail: the two adjacent
+matching digits /are not part of a larger group of matching digits/.
+
+Given this additional criterion, but still ignoring the range rule, the
+following are now true:
+
+- =112233= meets these criteria because the digits never decrease and
+  all repeated digits are exactly two digits long.
+- =123444= no longer meets the criteria (the repeated =44= is part of a
+  larger group of =444=).
+- =111122= meets the criteria (even though =1= is repeated more than
+  twice, it still contains a double =22=).
+
+/How many different passwords/ within the range given in your puzzle
+input meet all of the criteria?
+
+Your puzzle answer was =1419=.
diff --git a/2019/day04/aoc-c.c b/2019/day04/aoc-c.c
new file mode 100644
index 0000000..147b13b
--- /dev/null
+++ b/2019/day04/aoc-c.c
@@ -0,0 +1,103 @@
+/* aoc-c.c: Advent of Code 2019, day 3 parts 1 & 2
+ *
+ * Copyright (C) 2021 Bruno Raoult ("br")
+ * Licensed under the GNU General Public License v3.0 or later.
+ * Some rights reserved. See COPYING.
+ *
+ * You should have received a copy of the GNU General Public License along with this
+ * program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.html>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <malloc.h>
+#include <errno.h>
+#include <string.h>
+#include <getopt.h>
+
+#include "debug.h"
+
+static int is_valid(int number, int part)
+{
+    int valid = 0, dups[10] = { 0 };
+    int digit, dec;
+
+    for (digit = number % 10; number > 10; digit = dec) {
+        number /= 10;
+        dec = number % 10;
+        if (dec > digit)
+            return 0;
+        if (dec == digit) {
+            valid = 1;
+            dups[digit] += 2;
+        }
+    }
+    if (!valid)
+        return 0;
+    if (part == 2) {
+        valid = 0;
+        for (int i = 0; i < 10; ++i) {
+            if (dups[i] == 2)
+                return 1;
+        }
+    }
+    return valid;
+}
+
+static int doit(int *nums, int part)
+{
+    int res = 0;
+
+    /* There is surely a way to avoid 99% of useless calls to is_valid.
+     */
+    for (int i = nums[0]; i < nums[1]; ++i)
+        if (is_valid(i, part))
+            res++;
+    return res;
+}
+
+static int *parse(int *res)
+{
+    size_t alloc = 0;
+    char *buf = NULL;
+
+    getline(&buf, &alloc, stdin);
+    *res = atoi(strtok(buf, "-"));
+    *(res+1) = atoi(strtok(NULL, "-"));
+    free(buf);
+    return res;
+}
+
+static int usage(char *prg)
+{
+    fprintf(stderr, "Usage: %s [-d debug_level] [-p part]\n", prg);
+    return 1;
+}
+
+int main(int ac, char **av)
+{
+    int opt, part = 1;
+    int nums[2];
+
+    while ((opt = getopt(ac, av, "d:p:")) != -1) {
+        switch (opt) {
+            case 'd':
+                debug_level_set(atoi(optarg));
+                break;
+            case 'p':                             /* 1 or 2 */
+                part = atoi(optarg);
+                if (part < 1 || part > 2)
+            default:
+                    return usage(*av);
+        }
+    }
+    if (optind < ac)
+        return usage(*av);
+
+    parse(nums);
+    printf("%s : res=%d\n", *av, doit(nums, part));
+
+    exit (0);
+}