Compilare: main.cpp: In function 'void make_hash()': main.cpp:18:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<a.length();i++) ~^~~~~~~~~~~ main.cpp:23:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<a.length();i++) ~^~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:36:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<=b.size()-a.size();i++) ~^~~~~~~~~~~~~~~~~~~