Compilare: main.cpp: In function 'std::__cxx11::string invers(std::__cxx11::string)': main.cpp:19:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<a.size();i++) ~^~~~~~~~~ main.cpp: In function 'int main()': main.cpp:55:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(poz<=s.size()) ~~~^~~~~~~~~~ main.cpp:59:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(s.size()<poz) ~~~~~~~~^~~~ main.cpp:53:13: warning: unused variable 'k' [-Wunused-variable] char k; ^