Index: aoc.c
==================================================================
--- aoc.c
+++ aoc.c
@@ -1,27 +1,22 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-
-#include "aocutils.h"
 #include "aocdailies.h" // prototypes for all aocYYYYdd functions!
+#include "aocutils.h"
 
 #define MAX_YEAR 2024
 
 int main(int argc, char **argv) {
     unsigned y = 0, d = 0;
     char dataname[99];
     if (argc >= 3) {
         char *err;
         y = strtoul(argv[1], &err, 10);
-        if (err && *err) y = 0;
-        if (y < 2015) y = 0;
-        if (y > MAX_YEAR) y = 0;
+        if (*err || (y < 2015) || (y > MAX_YEAR)) y = 0;
         d = strtoul(argv[2], &err, 10);
-        if (err && *err) d = 0;
-        if (d < 1) d = 0;
-        if (d > 25) d = 0;
+        if (*err || (d < 1) || (d > 25)) d = 0;
         if (argc >= 4) {
             sprintf(dataname, "%.98s", argv[3]);
         } else {
             sprintf(dataname, ".%04u%02u.txt", y, d);
         }
@@ -38,8 +33,8 @@
     size_t ilen = slurp(&input, dataname);
 
     // call the right function
     aocfunc *p = aocselect(y, d);
     if (p) p(input, ilen);
-    else fprintf(stderr, "Impossible!\n");
+    else fprintf(stderr, "Error: aoc%04u%02u() is missing.\n", y, d);
     free(input);
 }

Index: aoc2024.c
==================================================================
--- aoc2024.c
+++ aoc2024.c
@@ -2,11 +2,10 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-
 #include "aocdailies.h"
 #include "aocutils.h"
 
 static size_t rcmap(unsigned size, unsigned row, unsigned col) {
     return row * (size + 1) + col;