Compilare: user.cpp: In function ‘void add_edges(int, int)’: user.cpp:96:9: warning: unused variable ‘i’ [-Wunused-variable] int i; ^ user.cpp: In function ‘int main()’: user.cpp:152:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < roots.size(); i++) add_edges(roots[i], i); ^ user.cpp:160:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < roots.size(); i++) ^ user.cpp:165:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < roots.size(); i++) ^ user.cpp:169:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < leaves.size(); i++) ^ user.cpp:173:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < roots.size(); i++) ^ user.cpp:178:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 1; i < paired.size(); i++) ^ user.cpp:184:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < unused[0].size(); i++) ^ user.cpp:131:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("plan.in","r",stdin); ^ user.cpp:132:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("plan.out","w",stdout); ^ user.cpp:134:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &n, &m); ^ user.cpp:136:30: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &x, &y); ^