Compilare: user.cpp: In function 'void read_data()': user.cpp:50: warning: format '%d' expects type 'int*', but argument 3 has type 'int' user.cpp: In function 'void write_data()': user.cpp:67: warning: format '%d' expects type 'int*', but argument 3 has type 'int' user.cpp:67: warning: format '%d' expects type 'int*', but argument 4 has type 'int' user.cpp:56: warning: unused variable 'j'