Compilare: user.cpp: In function ‘int main()’: user.cpp:19:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<s.length();++i){ ^ user.cpp:20:61: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(!x.empty()&&s[i]-'0'>x.top()&&x.size()+n-i-1>=m){x.pop();} ^ user.cpp:21:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(x.size()<m) x.push(s[i]-'0'); ^