Compilare: user.cpp: In function ‘bool check_parant(std::string)’: user.cpp:15:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j=1; j<=s.size(); ++j) ^ user.cpp:20:8: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if (s[j]==')') ^ user.cpp: In function ‘int main()’: user.cpp:36:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=1; i<s.size(); ++i) ^