Compilare: user.cpp: In function ‘void kruskall()’: user.cpp:55:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; tree.size() < N - 1 && i < M; ++i) { ^ user.cpp:69:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < tree.size(); ++i) { ^ user.cpp: In function ‘void readData()’: user.cpp:37:25: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen(IN, "r", stdin); ^ user.cpp:38:25: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf(" %d %d", &N, &M); ^ user.cpp:41:33: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf(" %d %d %d", &s, &c, &d); ^ user.cpp: In function ‘void kruskall()’: user.cpp:67:27: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen(OUT, "w", stdout); ^