Compilare: user.cpp: In function ‘int main()’: user.cpp:24:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0; i < strlen(s) ; ++i) ^ user.cpp:20:36: 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:21:38: 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:22:29: 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:23:12: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s); ^ /tmp/ccHtJA1g.o: In function `main': user.cpp:(.text.startup+0x74): warning: the `gets' function is dangerous and should not be used.