Compilare: user.c: In function 'main': user.c:63: warning: format '%s' expects type 'char *', but argument 3 has type 'char (*)[20]' user.c:71: warning: null argument where non-null required (argument 2) user.c:71: warning: null argument where non-null required (argument 2) user.c:77: warning: null argument where non-null required (argument 2) user.c:77: warning: null argument where non-null required (argument 2) user.c:86: warning: null argument where non-null required (argument 2) user.c:86: warning: null argument where non-null required (argument 2)