Compilare: user.cpp: In function ‘void back(int, int, int)’: user.cpp:20:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<v[a].size();i++) ^ user.cpp:28:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<v[a].size();i++) ^ user.cpp:29:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j=0;j<v[b].size();j++) ^ user.cpp: In function ‘int main()’: user.cpp:61:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<v[x].size();i++) ^ user.cpp:62:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j=i+1;j<v[x].size();j++) ^ user.cpp:42:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("ciclu2.in","r",stdin); ^ user.cpp:43:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("ciclu2.out","w",stdout); ^ user.cpp:44:25: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d",&n,&m); ^ user.cpp:47:30: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d",&x,&y); ^ user.cpp:51:19: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&m); ^ user.cpp:54:29: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d",&x,&y); ^