Ommitted parameter names is a C23 feature.

Index: main.c
--- main.c.orig
+++ main.c
@@ -37,7 +37,7 @@
 
 /** alarmInterrupt is used to print out the progress at specific intervals */
 static void
-alarmInterrupt(int) {
+alarmInterrupt(int dummy) {
   if(!printProgress())
     alarm(PRINTERVAL);
 }
