Compilare: main.cpp: In function 'int main()': main.cpp:20:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<s1.size(); i++) ~^~~~~~~~~~ main.cpp:28:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1; i<s.size()-1; i++) ~^~~~~~~~~~~ main.cpp:37:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=2; i<s.size()-1; i++) ~^~~~~~~~~~~