/in/foo.cc: In function 'int main()':
/in/foo.cc:7:32: error: 'setprecision' was not declared in this scope
     cout<<fixed<<setprecision(2)<<fabs(x1*(y2-y3)+x2*(y3-y1)+x3*(y1-y2))/2;
                                ^
/in/foo.cc:7:72: error: 'fabs' was not declared in this scope
     cout<<fixed<<setprecision(2)<<fabs(x1*(y2-y3)+x2*(y3-y1)+x3*(y1-y2))/2;
                                                                        ^