/in/foo.cc:4:1: error: 'longlong' does not name a type
 longlong a,b,c;
 ^~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:7:7: error: 'a' was not declared in this scope
  cin>>a>>b;
       ^
/in/foo.cc:7:10: error: 'b' was not declared in this scope
  cin>>a>>b;
          ^
/in/foo.cc:8:2: error: 'c' was not declared in this scope
  c=a*b-a-b;
  ^