Compilare: user.cpp: In function ‘void pref()’: user.cpp:19:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 2; i < a.length(); i++) { ^ user.cpp: In function ‘void kmp()’: user.cpp:28:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < b.length(); i++) { ^ user.cpp:32:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (k == a.length() - 1) { ^ user.cpp: In function ‘int main()’: user.cpp:54:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < sol.size(); i++) { ^ user.cpp:44:6: warning: unused variable ‘x’ [-Wunused-variable] int x, y; ^ user.cpp:44:9: warning: unused variable ‘y’ [-Wunused-variable] int x, y; ^