Compilare: user.cpp: In function ‘int main()’: user.cpp:15:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); ++i) ^ user.cpp:18:39: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses] else if (!s.empty() && (s[i] == '}' && t.top().first != '{' || s[i] == ']' && t.top().first != '[' || s[i] == ')' && t.top().first != '(')) ^ user.cpp:18:117: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses] else if (!s.empty() && (s[i] == '}' && t.top().first != '{' || s[i] == ']' && t.top().first != '[' || s[i] == ')' && t.top().first != '(')) ^