Compilare: user.cpp: In function ‘void write_data()’: user.cpp:53:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<coord.size();++i) ^ user.cpp: In function ‘int main()’: user.cpp:61:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<coord.size();++i); ^ user.cpp:64:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<coord.size();++i) ^