Compilare: main.cpp: In function 'int main()': main.cpp:123:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < n.size() / 2; i++) { ~~^~~~~~~~~~~~~~ main.cpp:132:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < n.size() / 2; i++) out << sol[i]; ~~^~~~~~~~~~~~~~