Compilare: user.c:11: warning: data definition has no type or storage class user.c:11: warning: type defaults to 'int' in declaration of 'M' user.c:11: warning: type defaults to 'int' in declaration of 'vm' user.c:11: warning: type defaults to 'int' in declaration of 'nr' user.c: In function 'main': user.c:39: warning: array subscript has type 'char' user.c:40: warning: array subscript has type 'char' user.c:45: warning: array subscript has type 'char' user.c:46: warning: array subscript has type 'char' user.c: In function 'back': user.c:70: warning: array subscript has type 'char' user.c:74: warning: array subscript has type 'char'