Compilare: main.cpp: In function 'int main()': main.cpp:30:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(st.size()<=revk) ~~~~~~~~~^~~~~~ main.cpp:17:36: 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); ^ main.cpp:18:38: 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); ^ main.cpp:21:24: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&n,&k); ^ main.cpp:22:19: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%s",ch); ^