Compilare: user.cpp: In function ‘int main()’: user.cpp:37:19: warning: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second: [enabled by default] L-=in.tellg()-1; ^ In file included from /usr/local/include/c++/4.8.0/iosfwd:40:0, from /usr/local/include/c++/4.8.0/ios:38, from /usr/local/include/c++/4.8.0/istream:38, from /usr/local/include/c++/4.8.0/fstream:38, from user.cpp:1: /usr/local/include/c++/4.8.0/bits/postypes.h:192:7: note: candidate 1: std::fpos<_StateT> std::fpos<_StateT>::operator-(std::streamoff) const [with _StateT = __mbstate_t; std::streamoff = long long int] operator-(streamoff __off) const ^ user.cpp:37:19: note: candidate 2: operator-(std::streamoff {aka long long int}, int) <built-in> L-=in.tellg()-1; ^ user.cpp:29:6: warning: unused variable ‘i’ [-Wunused-variable] int i , j ; ^ user.cpp:29:10: warning: unused variable ‘j’ [-Wunused-variable] int i , j ; ^