Update greedy_algorithms/digit_separation.cpp

Co-authored-by: realstealthninja <68815218+realstealthninja@users.noreply.github.com>

greedy_algorithms/digit_separation.cpp

@@ -138,6 +138,10 @@ void tests(){
 
     reverseOrder = ds.digitSeparationReverseOrder(number);
     assert(reverseOrder == expectedReverse);
+/**
+ * @brief main function
+ * @return 0 on successful exit
+ */
 int main() {
     tests(); // run self test implementation