Compilare: user.cpp: In function ‘void _transform(std::string&, std::string&)’: user.cpp:77:39: warning: array subscript has type ‘char’ [-Wchar-subscripts] if ( first_use[S.top()] < first_use[e] ) break; ^ user.cpp:77:54: warning: array subscript has type ‘char’ [-Wchar-subscripts] if ( first_use[S.top()] < first_use[e] ) break; ^ user.cpp:74:22: warning: unused variable ‘c’ [-Wunused-variable] char c = S.top(); ^ user.cpp: In function ‘void get_string(std::string&)’: user.cpp:41:21: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%s\n", s); ^ user.cpp: In function ‘int main()’: user.cpp:137:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("logic.in","r",stdin); ^ user.cpp:138:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("logic.out","w",stdout); ^ user.cpp:145:22: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n", &n); ^