/in/foo.cc: In function 'int main()':
/in/foo.cc:7:2: error: 'cin' was not declared in this scope
  cin>>a;
  ^~~
/in/foo.cc:7:2: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/7/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~
/in/foo.cc:11:25: error: invalid type argument of unary '*' (have 'double')
  s=((p-a)*(p-b)*(p-c))**0.5;
                         ^~~
/in/foo.cc:12:17: warning: spurious trailing '%' in format [-Wformat=]
  printf("s=d%",s);
                 ^
/in/foo.cc:12:17: warning: too many arguments for format [-Wformat-extra-args]