Compilare: main.cpp: In function 'int main()': main.cpp:21:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<a.length(); i++) ~^~~~~~~~~~~ main.cpp:32:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<a.length(); i++) ~^~~~~~~~~~~ main.cpp:42:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=a.length(); i<b.length(); i++) ~^~~~~~~~~~~