Compilare: user.cpp: In function ‘int main()’: user.cpp:33:30: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[k]=NULL; ^~~~ user.cpp:37:28: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[k+1]=NULL; ^~~~ user.cpp:41:30: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[k]=NULL; ^~~~ user.cpp:44:28: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[k+1]=NULL; ^~~~ user.cpp:8:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] { freopen("dir.in", "r",stdin); ^ user.cpp:9:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("dir.out", "w",stdout); ^