Compilare: user.cpp: In function ‘int main()’: user.cpp:18:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0; i <= strlen(s) ; ++i) ^ user.cpp:14:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("alibaba.in","r",stdin); ^ user.cpp:15:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("alibaba.out","w",stdout); ^ user.cpp:16:29: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%hd %hd\n",&n,&k); ^ user.cpp:17:12: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s); ^ /tmp/ccBOpoHF.o: In function `main': user.cpp:(.text.startup+0xc4): warning: the `gets' function is dangerous and should not be used.