retval(1): make C and Rust code similar

retval/retval.c

@@ -3,21 +3,22 @@
 #include <stdlib.h> /* strtol(3) */
 #include <sysexits.h> /* EX_USAGE */
 
-static char *program_name = "retval";
+int usage(char *s){
+	fprintf(stderr, "Usage: %s [status]\n", s == NULL ? "retval" : s);
+	return EX_USAGE;
+}
 
 int main(int argc, char *argv[]){
-	unsigned int s;
 
-	if(argc < 2)
-		goto usage;
-
-	errno = 0;
-	s = strtol(argv[1], &argv[1], 10);
-	if(*argv[1] != '\0' || errno != 0){
-usage:		fprintf(stderr, "Usage: %s [status]\n",
-			argv[0] == NULL ? program_name : argv[0]);
-		return EX_USAGE;
+	switch(argc){
+		case 2: { unsigned int s;
+			errno = 0;
+			s = strtol(argv[1], &argv[1], 10);
+			if(*argv[1] != '\0' || errno != 0){
+				return usage(argv[0]);
+			}
+			return s;
+		}
+		default: return usage(argv[0]);
 	}
-
-	return s;
 }