Language: C++

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace contest10
{
    class Program
    {
        static void Main(string[] args)
        {
            var read_line_origin = Console.ReadLine();

            if (string.IsNullOrEmpty(read_line_origin))
            {
                return;
            }

            //三角形の数
            int all_num = int.Parse(read_line_origin);

            
            //空白で分割する
            read_line_origin = Console.ReadLine();
            string[] words = read_line_origin.Split();

            for (int i = 0; i < all_num; i++)
            {
                //配列の要素、すべてに処理を行う
                var num_array = Array.ConvertAll(words, len => double.Parse(len));

                //三角形の座標
                double x1 = num_array[(i * 6) + 0];
                double y1 = num_array[(i * 6) + 1];
                double x2 = num_array[(i * 6) + 2];
                double y2 = num_array[(i * 6) + 3];
                double x3 = num_array[(i * 6) + 4];
                double y3 = num_array[(i * 6) + 5];

                //辺の長さ
                double r1 = Math.Sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
                double r2 = Math.Sqrt((x2 - x3) * (x2 - x3) + (y2 - y3) * (y2 - y3));
                double r3 = Math.Sqrt((x3 - x1) * (x3 - x1) + (y3 - y1) * (y3 - y1));

                //計算用
                double tmp_1 = (r1 * r1) * (r2 * r2 + r3 * r3 - r1 * r1);
                double tmp_2 = (r2 * r2) * (r3 * r3 + r1 * r1 - r2 * r2);
                double tmp_3 = (r3 * r3) * (r1 * r1 + r2 * r2 - r3 * r3);

                double tri_tmp = tmp_1 + tmp_2 + tmp_3;

                double center_x = (tmp_1 * x1 + tmp_2 * x2 + tmp_3 * x3) / tri_tmp;
                double center_y = (tmp_1 * y1 + tmp_2 * y2 + tmp_3 * y3) / tri_tmp;

                double x = (((x1 * x1 + y1 * y1) * (y2 - y3)) +
                            ((x2 * x2 + y2 * y2) * (y3 - y1)) +
                            ((x3 * x3 + y3 * y3) * (y1 - y2)))
                            /
                            ((x1 * (y2 - y3)) +
                             (x2 * (y3 - y1)) +
                             (x3 * (y1 - y2))
                            ) * 0.5;
                double y = (((x1 * x1 + y1 * y1) * (x2 - x3)) + ((x2 * x2 + y2 * y2) * (x3 - x1)) + ((x3 * x3 + y3 * y3) * (x1 - x2))) / ((y1 * (x2 - x3)) + (y2 * (x3 - x1)) + (y3 * (x1 - x2))) * 0.5;


                double radius = (r1 * r2 * r3) /
                                Math.Sqrt(
                                    (r1 + r2 + r3) * (-r1 + r2 + r3) * (r1 - r2 + r3) * (r1 + r2 - r3)

                                );

                Console.WriteLine("{0:f3} {1:f3} {2:f3}", x, y, radius);
            }




        }
    }
}

Compiler output:
a.cc:1:7: error: expected nested-name-specifier before 'System'
    1 | using System;
      |       ^~~~~~
a.cc:2:7: error: expected nested-name-specifier before 'System'
    2 | using System.Collections.Generic;
      |       ^~~~~~
a.cc:3:7: error: expected nested-name-specifier before 'System'
    3 | using System.Linq;
      |       ^~~~~~
a.cc:4:7: error: expected nested-name-specifier before 'System'
    4 | using System.Text;
      |       ^~~~~~
a.cc:10:26: error: 'string' has not been declared
   10 |         static void Main(string[] args)
      |                          ^~~~~~
a.cc:10:35: error: expected ',' or '...' before 'args'
   10 |         static void Main(string[] args)
      |                                   ^~~~
a.cc:79:6: error: expected ';' after class definition
   79 |     }
      |      ^
      |      ;
a.cc: In static member function 'static void contest10::Program::Main(int*)':
a.cc:12:13: error: 'var' was not declared in this scope
   12 |             var read_line_origin = Console.ReadLine();
      |             ^~~
a.cc:14:17: error: 'string' was not declared in this scope
   14 |             if (string.IsNullOrEmpty(read_line_origin))
      |                 ^~~~~~
a.cc:14:38: error: 'read_line_origin' was not declared in this scope
   14 |             if (string.IsNullOrEmpty(read_line_origin))
      |                                      ^~~~~~~~~~~~~~~~
a.cc:20:27: error: expected primary-expression before 'int'
   20 |             int all_num = int.Parse(read_line_origin);
      |                           ^~~
a.cc:24:13: error: 'read_line_origin' was not declared in this scope
   24 |             read_line_origin = Console.ReadLine();
      |             ^~~~~~~~~~~~~~~~
a.cc:24:32: error: 'Console' was not declared in this scope
   24 |             read_line_origin = Console.ReadLine();
      |                                ^~~~~~~
a.cc:25:13: error: 'string' was not declared in this scope
   25 |             string[] words = read_line_origin.Split();
      |             ^~~~~~
a.cc:25:20: error: expected primary-expression before ']' token
   25 |             string[] words = read_line_origin.Split();
      |                    ^
a.cc:30:21: error: expected ';' before 'num_array'
   30 |                 var num_array = Array.ConvertAll(words, len => double.Parse(len));
      |                     ^~~~~~~~~
a.cc:33:29: error: 'num_array' was not declared in this scope
   33 |                 double x1 = num_array[(i * 6) + 0];
      |                             ^~~~~~~~~
a.cc:41:29: error: 'Math' was not declared in this scope
   41 |                 double r1 = Math.Sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
      |                             ^~~~