Compilare: user.cpp: In function ‘int main()’: user.cpp:39: warning: operation on ‘nr’ may be undefined user.cpp:39: warning: operation on ‘nr’ may be undefined user.cpp:41: warning: operation on ‘nr’ may be undefined user.cpp:41: warning: operation on ‘nr’ may be undefined user.cpp:46: warning: operation on ‘nr’ may be undefined user.cpp:48: warning: operation on ‘nr’ may be undefined user.cpp:48: warning: operation on ‘nr’ may be undefined user.cpp:50: warning: operation on ‘nr’ may be undefined user.cpp:50: warning: operation on ‘nr’ may be undefined user.cpp:24: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result