Language: C++

#include <iostream>
#include <iomanip>
#include <vector>
#include <cmath>
using namespace std;
typedef vector <double> vd;
typedef vector <　vd　> vvd;

vvd inverse(vvd &x){
	vvd tmp(2, vd(2));
	if (x.size()!=2) return tmp;
	double a, b, c, d, e;
	a = x[0][0];
	b = x[0][1];
    c = x[1][0];
	d = x[1][1];
    e = 1.0 / (a*d-b*c);
	tmp[0][0] = d * e;
	tmp[0][1] = -b * e;
	tmp[1][0] = -c * e;
	tmp[1][1] = a * e;
	return tmp;
}

vvd Mmult(vvd &A, vvd &B){
    int n1=A.size();
    int n2=A[0].size();
	int n3=B[0].size();
	vvd C(n1, vd(n3));
	for (int i=0; i<n1; i++)
		for (int j=0; j<n3; j++)
			C[i][j] = 0;

    for (int i=0; i<n1; i++)
		for (int j=0; j<n2; j++)
			for (int k=0; k<n3; k++)
				C[i][k] += A[i][j] * B[j][k];
    return C;
}

int main(void){
    int n;
	double x1, y1, x2, y2, x3, y3, dx1, dy1, dx2, dy2;
	vvd A(2, vd(2)), B(2, vd(1));
	cin>>n;
	for (int i=1; i<n+1; i++){
		cin>>x1>>y1>>x2>>y2>>x3>>y3;
		dx1 = x2 - x1;
		dy1 = y2 - y1;
		dx2 = x3 - x1;
		dy2 = y3 - y1;
		A[0][0] = -dx1;
		A[0][1] = dy1;
		A[1][0] = -dx2;
		A[1][1] = dy2;
		B[0][0] = -dx1*(x1+x2)/2 + dy1*(y1+y2)/2;
		B[1][0] = -dx2*(x1+x3)/2 + dy2*(y1+y3)/2;
		B = Mmult(inverse(A), B);

		double r = pow(pow(B[0][0]-x1,2)+pow(B[1][0]-y1,2), 0.5);
	    cout<<fixed<<setprecision(3);
		cout<<B[0][0]<<" "<<B[1][0]<<" "<<r<<endl;
	}
    return 0;
}

Compiler output:
a.cc:7:17: error: extended character 　 is not valid in an identifier
    7 | typedef vector <　vd　> vvd;
      |                 ^
a.cc:7:17: error: extended character 　 is not valid in an identifier
a.cc:7:17: error: '\U00003000vd\U00003000' was not declared in this scope
    7 | typedef vector <　vd　> vvd;
      |                 ^~~~~~
a.cc:7:23: error: template argument 1 is invalid
    7 | typedef vector <　vd　> vvd;
      |                       ^
a.cc:7:23: error: template argument 2 is invalid
a.cc: In function 'vvd inverse(vvd&)':
a.cc:10:25: error: expression list treated as compound expression in initializer [-fpermissive]
   10 |         vvd tmp(2, vd(2));
      |                         ^
a.cc:10:20: error: cannot convert 'vd' {aka 'std::vector<double>'} to 'vvd' {aka 'int'} in initialization
   10 |         vvd tmp(2, vd(2));
      |                    ^~~~~
      |                    |
      |                    vd {aka std::vector<double>}
a.cc:11:15: error: request for member 'size' in 'x', which is of non-class type 'vvd' {aka 'int'}
   11 |         if (x.size()!=2) return tmp;
      |               ^~~~
a.cc:13:14: error: invalid types 'vvd {aka int}[int]' for array subscript
   13 |         a = x[0][0];
      |              ^
a.cc:14:14: error: invalid types 'vvd {aka int}[int]' for array subscript
   14 |         b = x[0][1];
      |              ^
a.cc:15:10: error: invalid types 'vvd {aka int}[int]' for array subscript
   15 |     c = x[1][0];
      |          ^
a.cc:16:14: error: invalid types 'vvd {aka int}[int]' for array subscript
   16 |         d = x[1][1];
      |              ^
a.cc:18:12: error: invalid types 'vvd {aka int}[int]' for array subscript
   18 |         tmp[0][0] = d * e;
      |            ^
a.cc:19:12: error: invalid types 'vvd {aka int}[int]' for array subscript
   19 |         tmp[0][1] = -b * e;
      |            ^
a.cc:20:12: error: invalid types 'vvd {aka int}[int]' for array subscript
   20 |         tmp[1][0] = -c * e;
      |            ^
a.cc:21:12: error: invalid types 'vvd {aka int}[int]' for array subscript
   21 |         tmp[1][1] = a * e;
      |            ^
a.cc: In function 'vvd Mmult(vvd&, vvd&)':
a.cc:26:14: error: request for member 'size' in 'A', which is of non-class type 'vvd' {aka 'int'}
   26 |     int n1=A.size();
      |              ^~~~
a.cc:27:13: error: invalid types 'vvd {aka int}[int]' for array subscript
   27 |     int n2=A[0].size();
      |             ^
a.cc:28:17: error: invalid types 'vvd {aka int}[int]' for array subscript
   28 |         int n3=B[0].size();
      |                 ^
a.cc:29:25: error: expression list treated as compound expression in initializer [-fpermissive]
   29 |         vvd C(n1, vd(n3));
      |                         ^
a.cc:29:19: error: cannot convert 'vd' {aka 'std::vector<double>'} to 'vvd' {aka 'int'} in initialization
   29 |         vvd C(n1, vd(n3));
      |                   ^~~~~~
      |                   |
      |                   vd {aka std::vector<double>}
a.cc:32:26: error: invalid types 'vvd {aka int}[int]' for array subscript
   32 |                         C[i][j] = 0;
      |                          ^
a.cc:37:34: error: invalid types 'vvd {aka int}[int]' for array subscript
   37 |                                 C[i][k] += A[i][j] * B[j][k];
      |                                  ^
a.cc:37:45: error: invalid types 'vvd {aka int}[int]' for array subscript
   37 |                                 C[i][k] += A[i][j] * B[j][k];
      |                                             ^
a.cc:37:55: error: invalid types 'vvd {aka int}[int]' for array subscript
   37 |                                 C[i][k] += A[i][j] * B[j][k];
      |                                                       ^
a.cc: In function 'int main()':
a.cc:44:23: error: expression list treated as compound expression in initializer [-fpermissive]
   44 |         vvd A(2, vd(2)), B(2, vd(1));
      |                       ^
a.cc:44:18: error: cannot convert 'vd' {aka 'std::vector<double>'} to 'vvd' {aka 'int'} in initialization
   44 |         vvd A(2, vd(2)), B(2, vd(1));
      |                  ^~~~~
      |                  |
      |                  vd {aka std::vector<double>}
a.cc:44:36: error: expression list treated as compound expression in initializer [-fpermissive]
   44 |         vvd A(2, vd(2)), B(2, vd(1));
      |                                    ^
a.cc:44:31: error: cannot convert 'vd' {aka 'std::vector<double>'} to 'vvd' {aka 'int'} in initialization
   44 |         vvd A(2, vd(2)), B(2, vd(1));
      |                               ^~~~~
      |                               |
      |                               vd {aka std::vector<double>}
a.cc:52:18: error: invalid types 'vvd {aka int}[int]' for array subscript
   52 |                 A[0][0] = -dx1;
      |                  ^
a.cc:53:18: error: invalid types 'vvd {aka int}[int]' for array subscript
   53 |                 A[0][1] = dy1;
      |                  ^
a.cc:54:18: error: invalid types 'vvd {aka int}[int]' for array subscript
   54 |                 A[1][0] = -dx2;
      |                  ^
a.cc:55:18: error: invalid types 'vvd {aka int}[int]' for array subscript
   55 |                 A[1][1] = dy2;
      |                  ^
a.cc:56:18: error: invalid types 'vvd {aka int}[int]' for array subscript
   56 |                 B[0][0] = -dx1*(x1+x2)/2 + dy1*(y1+y2)/2;
      |                  ^
a.cc:57:18: error: invalid types 'vvd {aka int}[int]' for array subscript
   57 |                 B[1][0] = -dx2*(x1+x3)/2 + dy2*(y1+y3)/2;
      |                  ^
a.cc:58:34: error: cannot bind non-const lvalue reference of type 'vvd&' {aka 'int&'} to an rvalue of type 'vvd' {aka 'int'}
   58 |                 B = Mmult(inverse(A), B);
      |                           ~~~~~~~^~~
a.cc:25:16: note:   initializing argument 1 of 'vvd Mmult(vvd&, vvd&)'
   25 | vvd Mmult(vvd &A, vvd &B){
      |           ~~~~~^
a.cc:60:37: error: invalid types 'vvd {aka int}[int]' for array subscript
   60 |                 double r = pow(pow(B[0][0]-x1,2)+pow(B[1][0]-y1,2), 0.5);
      |                                     ^
a.cc:60:55: error: invalid types 'vvd {aka int}[int]' for array subscript
   60 |                 double r = pow(pow(B[0][0]-x1,2)+pow(B[1][0]-y1,2), 0.5);
      |                                                       ^
a.cc:62:24: error: invalid types 'vvd {aka int}[int]' for array subscript
   62 |                 cout<<B[0][0]<<" "<<B[1][0]<<" "<<r<<endl;
      |                        ^
a.cc:62:38: error: invalid types 'vvd {aka int}[int]' for array subscript
   62 |                 cout<<B[0][0]<<" "<<B[1][0]<<" "<<r<<endl;
      |                                      ^