Compilare: user.c: In function ‘infix2postfix’: user.c:238:12: warning: array subscript has type ‘char’ [-Wchar-subscripts] digits[efx++] = ' '; ^ user.c:252:12: warning: array subscript has type ‘char’ [-Wchar-subscripts] digits[efx++] = ' '; ^ user.c:269:11: warning: array subscript has type ‘char’ [-Wchar-subscripts] digits[efx++] = c; ^ user.c:275:12: warning: array subscript has type ‘char’ [-Wchar-subscripts] digits[efx++] = ' '; ^ user.c:293:10: warning: array subscript has type ‘char’ [-Wchar-subscripts] digits[efx++] = ' '; ^ user.c: In function ‘eval’: user.c:198:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ user.c: In function ‘push’: user.c:426:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ user.c: In function ‘peek2’: user.c:490:1: warning: control reaches end of non-void function [-Wreturn-type] } ^