/in/foo.cc:4:10: error: 'student' was not declared in this scope
 bool cmp(student a,student b){
          ^~~~~~~
/in/foo.cc:4:20: error: 'student' was not declared in this scope
 bool cmp(student a,student b){
                    ^~~~~~~
/in/foo.cc:4:29: error: expression list treated as compound expression in initializer [-fpermissive]
 bool cmp(student a,student b){
                             ^
/in/foo.cc:7:16: error: expected unqualified-id before ')' token
 struct student(){
                ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:15:14: error: elements of array 'student s [sn]' have incomplete type
  student s[sn];
              ^
/in/foo.cc:15:14: error: storage size of 's' isn't known