Compilare: user.cpp: In function ‘int main()’: user.cpp:27:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<a.length(); ++i){ ^ user.cpp:32:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<a.length(); ++i) ^ user.cpp:38:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<b.length()-a.length()+1; ++i) ^