Compilare: user.cpp: In function ‘int main()’: user.cpp:19:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(a.length()>=n) ^ user.cpp:21:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<a.length()-n;++i) ^ user.cpp:13:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("blis.in","r",stdin); ^ user.cpp:14:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("blis.out","w",stdout); ^ user.cpp:15:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d ",&n); ^ user.cpp:16:33: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(aux,sizeof(aux),stdin); ^