Index: aoc.c
==================================================================
--- aoc.c
+++ aoc.c
@@ -36,43 +36,10 @@
     // read data from dataname into input
     char *input = NULL;
     size_t ilen = slurp(&input, dataname);
 
     // call the right function
-    void (*p)(char *, size_t) = NULL;
-    switch (y * 100 + d) {
-        default: fprintf(stderr, "no function for year %d and day %d\n", y, d);
-                 exit(EXIT_FAILURE);
-        #if 0
-        case 201501: p = aoc201501; break;
-        case 201502: p = aoc201502; break;
-        case 201503: p = aoc201503; break;
-        case 201504: p = aoc201504; break;
-        case 201505: p = aoc201505; break;
-        case 201506: p = aoc201506; break;
-        case 201507: p = aoc201507; break;
-        case 201508: p = aoc201508; break;
-        case 201509: p = aoc201509; break;
-        case 201510: p = aoc201510; break;
-        case 201511: p = aoc201511; break;
-        case 201512: p = aoc201512; break;
-        case 201513: p = aoc201513; break;
-        case 201514: p = aoc201514; break;
-        case 201515: p = aoc201515; break;
-        case 201516: p = aoc201516; break;
-        case 201517: p = aoc201517; break;
-        case 201518: p = aoc201518; break;
-        case 201519: p = aoc201519; break;
-        case 201520: p = aoc201520; break;
-        case 201521: p = aoc201521; break;
-        case 201522: p = aoc201522; break;
-        case 201523: p = aoc201523; break;
-        case 201524: p = aoc201524; break;
-        case 201525: p = aoc201525; break;
-        #endif
-
-        case 202401: p = aoc202401; break;
-        case 202402: p = aoc202402; break;
-    }
-    p(input, ilen);
+    void (*p)(char *, size_t) = select(y, d);
+    if (p) p(input, ilen);
+    else fprintf(stderr, "Impossible!\n");
     free(input);
 }

ADDED   aocdailies.c
Index: aocdailies.c
==================================================================
--- /dev/null
+++ aocdailies.c
@@ -0,0 +1,41 @@
+#include <stddef.h>
+#include "aocdailies.h"
+
+aocfunc *select(int y, int d) {
+    void (*p)(char *, size_t);
+    switch (y * 100 + d) {
+        default: return NULL;
+
+        #if 0
+        case 201501: p = aoc201501; break;
+        case 201502: p = aoc201502; break;
+        case 201503: p = aoc201503; break;
+        case 201504: p = aoc201504; break;
+        case 201505: p = aoc201505; break;
+        case 201506: p = aoc201506; break;
+        case 201507: p = aoc201507; break;
+        case 201508: p = aoc201508; break;
+        case 201509: p = aoc201509; break;
+        case 201510: p = aoc201510; break;
+        case 201511: p = aoc201511; break;
+        case 201512: p = aoc201512; break;
+        case 201513: p = aoc201513; break;
+        case 201514: p = aoc201514; break;
+        case 201515: p = aoc201515; break;
+        case 201516: p = aoc201516; break;
+        case 201517: p = aoc201517; break;
+        case 201518: p = aoc201518; break;
+        case 201519: p = aoc201519; break;
+        case 201520: p = aoc201520; break;
+        case 201521: p = aoc201521; break;
+        case 201522: p = aoc201522; break;
+        case 201523: p = aoc201523; break;
+        case 201524: p = aoc201524; break;
+        case 201525: p = aoc201525; break;
+        #endif
+
+        case 202401: p = aoc202401; break;
+        case 202402: p = aoc202402; break;
+    }
+    return p;
+}

Index: aocdailies.h
==================================================================
--- aocdailies.h
+++ aocdailies.h
@@ -1,8 +1,13 @@
 #ifndef AOCDAILY_H_INCLUDED
 #define AOCDAILY_H_INCLUDED
 
+#include <stddef.h>
+
+typedef void aocfunc(char *, size_t);
+aocfunc *select(int, int);
+
 #if 0
 void aoc201501(char *, size_t);
 void aoc201502(char *, size_t);
 void aoc201503(char *, size_t);
 void aoc201504(char *, size_t);