Compilare: user.cpp: In function ‘int main()’: user.cpp:23:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j = 1; j < a.size(); ++j) { ^ user.cpp:29:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(k = j = 0; j < s.size(); ++j) { ^ user.cpp:33:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(k == a.size()) { ^ user.cpp:41:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 1; i < s.size(); ++i) { ^