/in/foo.cc:4:7: error: 'n' was not declared in this scope
    4 | int f(n){
      |       ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:14:12: error: 'f' cannot be used as a function
   14 |   int a=f(P);
      |            ^
/in/foo.cc:16:14: error: expected ';' before '}' token
   16 |   cout<<(a%b)
      |              ^
      |              ;
   17 |  }
      |  ~