/in/foo.cc: In function 'int main()':
/in/foo.cc:7:5: error: 'doulb' was not declared in this scope
     doulb X1,Y1,X2,Y2,X3,Y3,p;
     ^~~~~
/in/foo.cc:8:10: error: 'x1' was not declared in this scope
     cin>>x1>>y1>>x2>>y2>>x3>>y3;
          ^~
/in/foo.cc:8:18: error: 'x2' was not declared in this scope
     cin>>x1>>y1>>x2>>y2>>x3>>y3;
                  ^~
/in/foo.cc:8:22: error: 'y2' was not declared in this scope
     cin>>x1>>y1>>x2>>y2>>x3>>y3;
                      ^~
/in/foo.cc:8:26: error: 'x3' was not declared in this scope
     cin>>x1>>y1>>x2>>y2>>x3>>y3;
                          ^~
/in/foo.cc:8:30: error: 'y3' was not declared in this scope
     cin>>x1>>y1>>x2>>y2>>x3>>y3;
                              ^~
/in/foo.cc:9:40: error: 'p' was not declared in this scope
     cout<<fixed<<setprecision(2)<<sqrt(p*(p-a)*(p-b)*(p-c));
                                        ^
/in/foo.cc:9:45: error: 'a' was not declared in this scope
     cout<<fixed<<setprecision(2)<<sqrt(p*(p-a)*(p-b)*(p-c));
                                             ^
/in/foo.cc:9:51: error: 'b' was not declared in this scope
     cout<<fixed<<setprecision(2)<<sqrt(p*(p-a)*(p-b)*(p-c));
                                                   ^
/in/foo.cc:9:57: error: 'c' was not declared in this scope
     cout<<fixed<<setprecision(2)<<sqrt(p*(p-a)*(p-b)*(p-c));
                                                         ^