Compilare: user.cpp: In function ‘void pref()’: user.cpp:16:31: 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:25:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < b.length(); i++) { ^ user.cpp:29:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (k == a.length() - 1) { ^ user.cpp: In function ‘int main()’: user.cpp:55:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < sol.size(); i++) { ^ user.cpp:43:6: warning: unused variable ‘x’ [-Wunused-variable] int x, y; ^ user.cpp:43:9: warning: unused variable ‘y’ [-Wunused-variable] int x, y; ^ user.cpp:44:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("strmatch.in","r",stdin); ^ user.cpp:45:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("strmatch.out","w",stdout); ^