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 <iostream>
#include <string>
#include <vector>

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

class Pos
{
public:
	int x, y;
};

void solve()
{
	int d;
	cin >> d;
	bool first = true;
	while(d--)
	{
		if(!first)
		{
			cout << endl;
		}
		first = false;
		int n;
		cin >> n;
		if(n == 1)
		{
			cout << "#" << endl;
			continue;
		}
		else if(n == 2)
		{
			cout << "##" << endl;
			cout << "# " << endl;
			continue;
		}
		vector< vector<char> > field(n, vector<char>(n, ' '));
		for(int i = 0; i < n; ++i)
		{
			field[i][0] = '#';
			field[i][n - 1] = '#';
			field[0][i] = '#';
		}
		int direction = 0;
		Pos current;
		current.x = n - 1;
		current.y = n - 1;
		while(true)
		{
			Pos next;
			next.x = current.x + dx[direction];
			next.y = current.y + dy[direction];
			int count = 0;
			while(field[next.y + dy[direction]][next.x + dx[direction]] != '#')
			{
				field[next.y][next.x] = '#';
				current = next;
				next.x = current.x + dx[direction];
				next.y = current.y + dy[direction];
				++count;
			}
			direction = (direction + 1) % 4;
			if(count < 2)
			{
				break;
			}
		}
		for(int i = 0; i < n; ++i)
		{
			for(int j = 0; j < n; ++j)
			{
				cout << field[i][j];
			}
			cout << endl;
		}
	}
}

int main()
{
	solve();
	return(0);
}

C++: #include<iostream>
using namespace std;
#define MAX_D 101


bool dx[MAX_D][MAX_D];

void resetDx();
void makeDx();
void dispDx();
bool checkField(int n);
void make2();
int d;

int main(){
    int n;
    cin >>n;
    for(int i = 0; i < n; i++){
        resetDx();
        cin >>d;
        if(d == 2){
            make2();
        } else{
        makeDx();
        }
    }
    return 0;
}

void resetDx(){
    for(int i = 0; i < MAX_D; i++){
        for(int j = 0; j < MAX_D; j++){
            dx[i][j] = false;
        }
    }
}

void dispDx(){
    for(int i = 0; i < d; i++){
        for(int j = 0; j < d; j++){
            if(dx[i][j] == true) cout <<'#';
            else cout <<' ';
        }
        cout <<endl;
    }
}

void makeDx(){
    for(int i = 0; i < d; i++){
        dx[i][0] = true;
        dx[0][i] = true;
        dx[i][d - 1] = true;
    }
    int x = d - 1, y = d - 1, mx[4] = {-1, 0, 1, 0}, my[4] = {0, -1, 0, 1}, i = 0;
    bool moveFlg = false;
    while(true){
        while(checkField(x + mx[i]) && checkField(y + my[i]) && !dx[y + my[i] + my[i]][x + mx[i] + mx[i]]){
            if(!moveFlg) moveFlg = true;
            dx[y + my[i]][x + mx[i]] = true;
            x += mx[i]; y += my[i];
        }
        if(!moveFlg) break;
        //cout <<"now = " <<y <<", " <<x <<" iBefore = " <<i <<endl;
        i = (i + 1) % 4;
        int conti = (i + 2) % 4;
        int ny = y + my[i], nx = x + mx[i];
        bool endFlg = false;
        //cout <<"ny = " <<y <<"+" <<my[i] <<"=" <<ny <<", nx = " <<x <<"+" <<mx[i] <<"=" <<nx <<endl;
        for(int j = 0; j < 4; j++){
            if(j == conti) continue;
            else{
                if(checkField(ny + my[j]) && checkField(nx + mx[j])){
                    //cout <<"j = " <<j <<" ny + my[j] = " <<ny + my[j] <<", nx + mx[j] = " <<nx + mx[j];
                    if(dx[ny + my[j]][nx + mx[j]]){
                        //cout <<" true" <<endl;
                        endFlg = true;
                        break;
                    } else{
                        //cout <<" false" <<endl;
                    }
                }
            }
        }
        if(endFlg){
            break;
        }
        //dispDx();
    }
    dispDx();
}

bool checkField(int n){
    bool ret = true;
    if(n < 0 || n >= d) ret = false;
    return ret;
}

void make2(){
    for(int i = 0; i < 2; i++){
        for(int j = 0; j < 2; j++){
            if(i == 1 && j == 1){
            } else{
                cout <<'#';
            }
        }
        cout <<endl;
    }
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <cstring>

using namespace std;

char field[101][101];

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

bool check(int x,int y,int angle){
	if(!(y>=0&&x>=0&&y<n&&x<n)){
		return false;
	}

	for(int i = 0; i < 4; i++){
		if(angle==i)
			continue;
		int nx=dx[i]+x;
		int ny=dy[i]+y;
		if(!(ny>=0&&nx>=0&&ny<n&&nx<n)){
			continue;
		}
		if(field[ny][nx]=='#'){
			return false;
		}
	}
	return true;
}

int main(){

	int nn;
	cin>>nn;
	for(int i = 0; i < nn; i++){
		if(i!=0)
			cout<<endl;
		cin>>n;
		for(int j = 0; j < n; j++){
			for(int k = 0; k < n; k++){
				field[j][k]=' ';
			}
		}

		// 0:ツ右,1:ツ可コ,2:ツ債カ,3:ツ湘」
		int angle=3;
		int cx=0;
		int cy=n-1;
		int cnt=0;
		field[cy][cx]='#';
		while(1){
			if(angle==3){
				int ny=cy-1;
				int nx=cx;
				if(check(nx,ny,angle)){
					field[ny][nx]='#';
					cnt=0;
					cy=ny;
					cx=nx;
				}
				else{
					if(cnt>=1){
						break;
					}
					cnt++;
					angle=0;
				}
			}
			else if(angle==2){
				int ny=cy;
				int nx=cx-1;
				if(check(nx,ny,angle)){
					field[ny][nx]='#';
					cnt=0;
					cy=ny;
					cx=nx;
				}
				else{
					if(cnt>=1){
						break;
					}
					cnt++;
					angle=3;
				}
			}
			else if(angle==1){
				int ny=cy+1;
				int nx=cx;
				if(check(nx,ny,angle)){
					field[ny][nx]='#';
					cnt=0;
					cy=ny;
					cx=nx;
				}
				else{
					if(cnt>=1){
						break;
					}
					cnt++;
					angle=2;
				}
			}
			else if(angle==0){
				int ny=cy;
				int nx=cx+1;
				if(check(nx,ny,angle)){
					field[ny][nx]='#';
					cnt=0;
					cy=ny;
					cx=nx;
				}
				else{
					if(cnt>=1){
						break;
					}
					cnt++;
					angle=1;
				}
			}
		}
		for(int j = 0; j < n; j++){
			for(int k = 0; k < n; k++){
				cout<<field[j][k];
			}
			cout<<endl;
		}
	}

	return 0;
}