Language: C++

#include<stdio.h>
#include<math.h>
double x1, y1, x2, y2, x3, y3;
double px, py;
int main()
{
    int n;
    scanf("%d",&n);
    while(n--)
    {
        scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);
        double A1 =(x2*x2+y2*y2-x1*x1-y1*y1)*(y3-y1);
        double B1 =(x3*x3+y3*y3-x1*x1-y1*y1)*(y2-y1);
        double A2 =(x3*x3+y3*y3-x1*x1-y1*y1)*(x2-x1);
        double B2 =(x2*x2+y2*y2-x1*x1-y1*y1)*(x3-x1);
        double D = (x2-x1)*(y3-y1)-(y2-y1)*(x3-x1);
        double X=(double)(A1-B1)/D/2;
        double Y=(double)(A2-B2)/D/2;
        double R = sqrt((X-x1)*(X-x1)+(Y-y1)*(Y-y1));
        printf("%.3f %.3f %.3f\n",X,Y,R);
    }
    return 0;
}

Compiler output:
a.cc:3:12: error: 'double y1' redeclared as different kind of entity
    3 | double x1, y1, x2, y2, x3, y3;
      |            ^~
In file included from /usr/include/features.h:523,
                 from /usr/include/x86_64-linux-gnu/bits/libc-header-start.h:33,
                 from /usr/include/stdio.h:28,
                 from a.cc:1:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:257:1: note: previous declaration 'double y1(double)'
  257 | __MATHCALL (y1,, (_Mdouble_));
      | ^~~~~~~~~~
a.cc: In function 'int main()':
a.cc:12:41: error: invalid operands of types 'double(double) noexcept' and 'double(double) noexcept' to binary 'operator*'
   12 |         double A1 =(x2*x2+y2*y2-x1*x1-y1*y1)*(y3-y1);
      |                                       ~~^~~
      |                                       |  |
      |                                       |  double(double) noexcept
      |                                       double(double) noexcept
a.cc:12:49: error: invalid operands of types 'double' and 'double(double) noexcept' to binary 'operator-'
   12 |         double A1 =(x2*x2+y2*y2-x1*x1-y1*y1)*(y3-y1);
      |                                               ~~^~~
      |                                               |  |
      |                                               |  double(double) noexcept
      |                                               double
a.cc:13:41: error: invalid operands of types 'double(double) noexcept' and 'double(double) noexcept' to binary 'operator*'
   13 |         double B1 =(x3*x3+y3*y3-x1*x1-y1*y1)*(y2-y1);
      |                                       ~~^~~
      |                                       |  |
      |                                       |  double(double) noexcept
      |                                       double(double) noexcept
a.cc:13:49: error: invalid operands of types 'double' and 'double(double) noexcept' to binary 'operator-'
   13 |         double B1 =(x3*x3+y3*y3-x1*x1-y1*y1)*(y2-y1);
      |                                               ~~^~~
      |                                               |  |
      |                                               |  double(double) noexcept
      |                                               double
a.cc:14:41: error: invalid operands of types 'double(double) noexcept' and 'double(double) noexcept' to binary 'operator*'
   14 |         double A2 =(x3*x3+y3*y3-x1*x1-y1*y1)*(x2-x1);
      |                                       ~~^~~
      |                                       |  |
      |                                       |  double(double) noexcept
      |                                       double(double) noexcept
a.cc:15:41: error: invalid operands of types 'double(double) noexcept' and 'double(double) noexcept' to binary 'operator*'
   15 |         double B2 =(x2*x2+y2*y2-x1*x1-y1*y1)*(x3-x1);
      |                                       ~~^~~
      |                                       |  |
      |                                       |  double(double) noexcept
      |                                       double(double) noexcept
a.cc:16:31: error: invalid operands of types 'double' and 'double(double) noexcept' to binary 'operator-'
   16 |         double D = (x2-x1)*(y3-y1)-(y2-y1)*(x3-x1);
      |                             ~~^~~
      |                             |  |
      |                             |  double(double) noexcept
      |                             double
a.cc:16:39: error: invalid operands of types 'double' and 'double(double) noexcept' to binary 'operator-'
   16 |         double D = (x2-x1)*(y3-y1)-(y2-y1)*(x3-x1);
      |                                     ~~^~~
      |                                     |  |
      |                                     |  double(double) noexcept
      |                                     double
a.cc:19:41: error: invalid operands of types 'double' and 'double(double) noexcept' to binary 'operator-'
   19 |         double R = sqrt((X-x1)*(X-x1)+(Y-y1)*(Y-y1));
      |                                        ~^~~
      |                                        | |
      |                                        | double(double) noexcept
      |                                        double
a.cc:19:48: error: invalid operands of types 'double' and 'double(double) noexcept' to binary 'operator-'
   19 |         double R = sqrt((X-x1)*(X-x1)+(Y-y1)*(Y-y1));
      |                                               ~^~~
      |                                               | |
      |                                               | double(double) noexcept
      |                                               double