always use gcc, fix warnings of func without prototype

weirdest warning.

Makefile

@@ -1,5 +1,5 @@
-CC = cc
-CC_FLAGS = 
+CC = gcc
+CC_FLAGS = -Wall -pedantic -std=c18
 
 SRC_FOLDER= ./src
 SRC_MAIN = hashtables.c
@@ -15,15 +15,15 @@ default: clean run
 
 build: $(SRC)
 	mkdir -p $(BIN_FOLDER)
-	$(CC) $(SRC) `$(CC_FLAGS)` -o $(BIN)
+	$(CC) $(SRC) $(CC_FLAGS) -o $(BIN)
 
 run: build
 	$(BIN)
 
 clean:
 	rm -rf $(BIN_FOLDER)
 
-valgrind:
+valgrind: $(SRC)
 	mkdir -p $(BIN_FOLDER)
-	gcc $(SRC) -Wall -pedantic -g -ggdb -O0 -std=c18 -o $(DEBUG_BIN)
+	gcc $(SRC) $(CC_FLAGS) -g -ggdb -O0 -o $(DEBUG_BIN)
 	valgrind $(DEBUG_BIN)

src/hashtables.c

@@ -57,7 +57,7 @@ struct HashStrSetValuesIterator
  *
  * @return HashStrSet instance, empty.
  */
-HashStrSet *hashstrset_init()
+HashStrSet *hashstrset_init(void)
 {
     HashStrSet *set = malloc(sizeof(HashStrSet));
     set->cardinality = 0;
@@ -180,7 +180,7 @@ bool hashstrset_remove(HashStrSet *set, char *value)
  *
  * @return HashStrSetValuesIterator instance, empty, ready to seek the set elements until its end.
  */
-HashStrSetValuesIterator *hashstrset_values_iterator()
+HashStrSetValuesIterator *hashstrset_values_iterator(void)
 {
     HashStrSetValuesIterator *iterator = malloc(sizeof(HashStrSetValuesIterator));
     iterator->current_value = NULL;
@@ -234,7 +234,7 @@ bool hashstrset_values_iterator_seek(HashStrSet *set, HashStrSetValuesIterator *
 /**
  * @brief Experimental execution.
  */
-int main()
+int main(void)
 {
     // create set
     HashStrSet *weekdays_set = hashstrset_init();