Compilare: user.cpp: In function ‘int main()’: user.cpp:25:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int k=0;k<r[j].size();++k) { ^ user.cpp:8:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("radixsort.in","r",stdin); ^ user.cpp:9:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("radixsort.out","w",stdout); ^ user.cpp:13:34: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d%d%d",&N,&A,&B,&C); ^