Compilare: main.cpp: In function 'std::__cxx11::string solve(std::__cxx11::string)': main.cpp:54:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (j < f[ch - 'A'].size()) expresie = expresie + f[ch - 'A'][j++]; ~~^~~~~~~~~~~~~~~~~~~~ main.cpp:56:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < apel.size()) ~~^~~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:90:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 2; j < aux.size(); ++j) ian = ian + aux[j]; ~~^~~~~~~~~~~~ main.cpp:98:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < fa.size(); ++i) ~~^~~~~~~~~~~ main.cpp:114:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int k = 0; k < sol.size(); ++k) stiva[++top] = sol[k]; ~~^~~~~~~~~~~~