I get this error ORA-00907: the right bracket is missing

Question

create table passenger(pnr number(10) primary key,
trainnumber number(5) foreign key references train(trainnumber),
noofseats number(4),
price number(4),
doj varchar2(10))

ORA-00907: missing right parentheses

Answer 1

The expression foreign keyis redundant (read: incorrect). The syntax is just to add references:

create table passenger(pnr number(10) primary key,
trainnumber number(5) references train(trainnumber), -- here
noofseats number(4),
price number(4),
doj varchar2(10))

Answer 2

change yout instruction CREATE TABLEas below

create table passenger(pnr number(10) primary key,
trainnumber number(5), 
noofseats number(4),
price number(4),
doj varchar2(10),
foreign key (trainnumber) references train(trainnumber))