/in/foo.cc: In function 'int main()':
/in/foo.cc:7:34: error: 'b' was not declared in this scope
  cout<<fixed<<setprecision(2)<<a+b;
                                  ^
/in/foo.cc:5:10: warning: unused variable 'sum' [-Wunused-variable]
  int n,a,sum=0;
          ^~~