Go: package main

import (
	"bufio"
	"os"
	"strconv"
	"fmt"
	)

var scanner = bufio.NewScanner(os.Stdin)

func main() {
	out := make([][]string, 100)
	for i := range out {
		out[i] = make([]string, 101)
	}
	dx := []int{0, 1, 0, -1}
	dy := []int{-1, 0, 1, 0}
	scanner.Scan()
	a, _ := strconv.Atoi(scanner.Text())
	for a > 0 {
		a--
		scanner.Scan()
		b, _ := strconv.Atoi(scanner.Text())
		for i := 0; i < b; i++ {
			for j := 0; j < b; j++ {
				out[i][j] = " "
			}
			out[i][b] = "0"
		}
		if b == 1 {
			fmt.Println("#")
			if a != 0 {
				fmt.Println()
			}
			continue
		}
		if b == 2 {
			fmt.Printf("##\n# \n")
			if a != 0 {
				fmt.Println()
				continue
			}
		}
		row := b -1
		col := 0
		dir := 0
		l := 0
		out[row][col] = "#"
		for {
			nrow := row+dy[dir%4]
			ncol := col+dx[dir%4]
			if dir%4 == 0 && nrow == 0 || dir%4==3&&ncol==0 || dir%4==2&&nrow==b-1 || dir%4==1&&ncol==b-1 {
				row=nrow
				col=ncol
				out[row][col]="#"
				dir++
				l = 1
			} else if out[nrow+dy[dir%4]][ncol+dx[dir%4]]=="#" {
				if l < 3 {
					break
				}
				dir++
				l = 1
			} else {
				row=nrow
				col=ncol
				out[row][col]="#"
				l++
			}
		}
		for i := 0; i < b; i++ {
			for j := 0; j < b; j++ {
				fmt.Printf("%s", out[i][j])
			}
			fmt.Println()
		}
		if a != 0 {
			fmt.Println()
		}
	}
}

C++: #include<bits/stdc++.h>
#define range(i,a,b) for(int i = (a); i < (b); i++)
#define rep(i,b) range(i,0,b)
#define pb(a) push_back(a)
#define all(a) (a).begin(), (a).end()
#define debug(x) cout << "debug " << x << endl;
#define INF (1 << 30)
using namespace std;

void solve(char a[105][105], int inp, int d, int y, int x){
    int i;
    for(i = 0; i < inp - 1; i++){
        a[y][x] = '#';
        if(d == 0){
            if(a[y - 2][x] == '#') break;
            y--;
        }else if(d == 1){
            if(a[y][x + 2] == '#') break;
            x++;
        }else if(d == 2){
            if(a[y + 2][x] == '#') break;
            y++;
        }else{
            if(a[y][x - 2] == '#') break;
            x--;
        }
    }
    if(i <= 1) return;
    solve(a, inp, (d + 1) % 4, y, x);

}

int main(){
    int n;
    char a[105][105];
    cin >> n;
    rep(i,n){
        if(i) cout << endl;
        rep(i,105) rep(j,105) a[i][j] = ' ';
        int inp;
        cin >> inp;
        solve(a, inp, 0, 104, 0);
        if(inp == 1) cout << '#' << endl;
        else if(inp == 2) cout << "# " << endl << "# " << endl;
        else{
            for(int i = 104 - inp + 1; i <= 104; i++){
                rep(j,inp){
                    cout << a[i][j];
                }
                cout << endl;
            }
        }
    }
}

C++: #include <iostream>
using namespace std;

class Guruguru
{
public:
  Guruguru(int n);
  ~Guruguru();

  void Show();

private:
  char** m_guruguru;
  int m_n;
  int m_now_i;
  int m_now_j;
  int m_direction;    //  0:上 1:右 2:下 3:左

  void make_guruguru();
  void put_point();
  void move_point();
  void change_direction();
  bool check_point();
};

Guruguru::Guruguru(int n)
{
  m_n = n;
  m_guruguru = new char*[m_n];
  for (int i=0; i<m_n; i++)
  {
    m_guruguru[i] = new char[m_n];
  }

  for (int i=0; i<n; i++)
  {
    for (int j=0; j<n; j++)
    {
      m_guruguru[i][j] = ' ';
    }
  }

  m_now_i = m_n-1;
  m_now_j = 0;
  m_direction = 0;
  make_guruguru();
}

Guruguru::~Guruguru()
{
  for (int i=0; i<m_n; i++)
  {
    delete[] m_guruguru[i];
  }
  delete[] m_guruguru;
}

void Guruguru::make_guruguru()
{
  int num = 0;
  while(true)
  {
    put_point();
    if (! check_point() )
    {
      if ( num == m_n-1 ) return;
      change_direction();
      num++;
    }
    move_point();
  }
}

void Guruguru::put_point()
{
  m_guruguru[m_now_i][m_now_j] = '#';
}

void Guruguru::move_point()
{
  switch(m_direction)
  {
  case 0:
    m_now_i--;
    break;
  case 1:
    m_now_j++;
    break;
  case 2:
    m_now_i++;
    break;
  case 3:
    m_now_j--;
    break;
  }
}

void Guruguru::change_direction()
{
  switch(m_direction)
  {
  case 3:
    m_direction = 0;
    break;
  default:
    m_direction++;
    break;
  }
}

bool Guruguru::check_point()
{
  int next_i = m_now_i;
  int next_j = m_now_j;
  int next_next_i = next_i;
  int next_next_j = next_j;
  switch(m_direction)
  {
  case 0:
    next_i--;
    next_next_i-=2;
    break;
  case 1:
    next_j++;
    next_next_j+=2;
    break;
  case 2:
    next_i++;
    next_next_i+=2;
    break;
  case 3:
    next_j--;
    next_next_j-=2;
    break;
  }
  if ( next_i < 0 || m_n <= next_i || next_j < 0 || m_n <= next_j )
  {
    return false;
  }
  else if ( next_next_i < 0 || m_n <= next_next_i || next_next_j < 0 || m_n <= next_next_j )
  {
    return true;
  }
  else
  {
    if ( '#' == m_guruguru[next_next_i][next_next_j] )
    {
      return false;
    }
    return true;
  }
}

void Guruguru::Show()
{
  for (int i=0; i<m_n; i++)
  {
    for (int j=0; j<m_n; j++)
    {
      cout << m_guruguru[i][j] << flush;
    }
    cout << endl;
  }
}

int main()
{
  int d;  //  データセットの個数
  cin >> d;
  for (int dataset=0; dataset<d; dataset++)
  {
    int n;  //  辺の長さ
    cin >> n;
    Guruguru guruguru(n);

    guruguru.Show();
  }
}

C++: #include <iostream>
using namespace std;

int main()
{
	int d;

	while( cin >> d ){
		for( int i = 0; i < d; ++i ){
			if( i != 0 ) cout << endl;
			int n;
			cin >> n;

			int size = n + 4;
			char* map = new char[ size * size ]();
			for( int j = 0; j < size; ++j ){
				for( int k = 0; k < size; ++k ){
					map[ j * size + k ] = ' ';
				}
			}
			for( int j = 0; j < size; ++j ){
				map[ j ] = map[ ( size - 1 ) * size + j ] = map[ size * j ] = map[ ( j + 1 ) * size - 1 ] = '#';
			}
			for( int j = 2; j < size - 2; ++j ){
				map[ j * size + 2 ] = '#';
			}
			int x = 2, y = 2;
			int dir = 1;
			int dirCount = 0;
			int straightCount = 0;
			while( dirCount < 2 ){
				map[ y * size + x ] = '#';
				++straightCount;
				int nx, ny;
				switch( dir ){
					case 0: nx = x; ny = y - 2; break;
					case 1: nx = x + 2; ny = y; break;
					case 2: nx = x; ny = y + 2; break;
					case 3: nx = x - 2; ny = y; break;
				}
				if( map[ ny * size + nx ] == '#' ){
					if( straightCount < 3 ){
						break;
					}
					dir = ( dir + 1 ) % 4;
					++dirCount;
					straightCount = 0;
					continue;
				}else{
					dirCount = 0;
				}
				switch( dir ){
					case 0: y -= 1; break;
					case 1: x += 1; break;
					case 2: y += 1; break;
					case 3: x -= 1; break;
				}
			}

			for( int p = 2; p < size - 2; ++p ){
				for( int q = 2; q < size - 2; ++q ){
					cout << map[ p * size + q ];
				}
				if( p != size - 3 ) cout << endl;
			}

			delete[] map;
		}
	}

	return 0;
}

C++: #include <bits/stdc++.h>
#define rep(i,a,n) for(int i=a;i<n;i++)
#define repb(i,a,b) for(int i=a;i>=b;i--)
#define all(a) a.begin(),a.end()
#define o(a) cout<<a<<endl
#define int long long
#define fi first
#define se second
using namespace std;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;

int h, w;

bool can(int y, int x){
	return (0 <= y && y < h && 0 <= x && x < w);
}

int dy[4] = {-1, 0, 1, 0};
int dx[4] = {0, 1, 0, -1};

signed main() {
	int t, n;
	cin >> t;
	rep(k, 0, t){
		if(k) cout << endl;
		int a[110][110]={};
		cin >> n;
		h = w = n;
		vi d;
		int tmp = n;
		d.push_back(tmp);
		while(1){
			if(tmp <= 2){
				d.push_back(tmp);
				break;
			}
			rep(i,0,2) d.push_back(tmp);
			tmp -= 2;
		}
		int y = n - 1, x = 0;
		a[y][x] = 1;
		rep(i, 0, d.size()){
			int dir = i % 4;
			rep(j, 0, d[i] - 1){
				y += dy[dir];
				x += dx[dir];
				a[y][x] = 1;
			}
		}
		rep(i, 0, n){
			rep(j, 0, n){
				cout << (a[i][j] ? "#":" ") ;
			}
			cout << endl;
		}
	}
}