Compilare: user.cpp: In function ‘void Backtracking(int, int, int)’: user.cpp:71:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (which == v.size()) ^ user.cpp: In function ‘int main()’: user.cpp:116:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (v.size() > 4 * k) { ^ user.cpp: In function ‘char Advance()’: user.cpp:26:38: warning: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fread(buffer, 1, SIZE, stdin); ^ user.cpp: In function ‘int main()’: user.cpp:97:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("union.in", "r", stdin); ^ user.cpp:98:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("union.out", "w", stdout); ^ user.cpp:100:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &tests); ^ user.cpp:103:38: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d%d\n", &n, &m, &k); ^ user.cpp:105:36: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%s\n", a[i] + 1); ^