foo.cc: In function 'int main()':
foo.cc:8:5: error: 'cin' was not declared in this scope
    8 |     cin >>X1>>Y1>>X2>>Y2>>X3>>Y3;
      |     ^~~
foo.cc:3:1: note: 'std::cin' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
    2 | #include <cmath>
  +++ |+#include <iostream>
    3 | using namespace std;
foo.cc:13:5: error: 'cout' was not declared in this scope
   13 |     cout<<fixed<<setprecision(2)<<sqrt(p*(p-a)*(p-b)*(p-c));
      |     ^~~~
foo.cc:13:5: note: 'std::cout' is defined in header '<iostream>'; did you forget to '#include <iostream>'?

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