Compilare: main.cpp: In function 'int main()': main.cpp:24:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<k.size(); i++) ~^~~~~~~~~ main.cpp:28:22: warning: suggest parentheses around '&&' within '||' [-Wparentheses] if(k[i]==')' && S.top().second=='(' main.cpp:30:22: warning: suggest parentheses around '&&' within '||' [-Wparentheses] || k[i]=='}' && S.top().second=='{')