Compilare: main.cpp: In function 'bool bt()': main.cpp:24:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(aux.length()==len && k>len) ~~~~~~~~~~~~^~~~~ main.cpp:26:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(k>len && aux.length()>len) ~~~~~~~~~~~~^~~~ main.cpp:28:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(aux.length()<k) ~~~~~~~~~~~~^~ main.cpp: In function 'int main()': main.cpp:67:34: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("perle.in","r",stdin); ^ main.cpp:68:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("perle.out","w",stdout); ^