Go: package main

import (
	"bufio"
	"encoding/json"
	"fmt"
	"os"
	"strconv"
	"strings"
)

var (
	sc = bufio.NewScanner(os.Stdin)
)

type Color int

const (
	ColorBlack Color = iota
	ColorRed
)

var strByColor = map[Color]string{
	ColorBlack: "black",
	ColorRed:   "red",
}

func (c Color) String() string {
	return strByColor[c]
}

type Node struct {
	ID      int
	X, Y    int
	Color   Color
	NextIDs map[int]struct{}
}

func (n *Node) String() string {
	d, _ := json.Marshal(n)
	return string(d)
}

type Map struct {
	Width, Height int
	Nodes         map[int]*Node
}

func (m *Map) GetByID(id int) *Node {
	return m.Nodes[id]
}

func (m *Map) Get(x, y int) *Node {
	return m.Nodes[m.getID(x, y)]
}

func (m *Map) SetColor(x, y int, c Color) {
	m.Nodes[m.getID(x, y)].Color = c
}

func (m *Map) getID(x, y int) int {
	return x + y*m.Width
}

func (m *Map) init() {
	for x := 1; x <= m.Width; x++ {
		for y := 1; y <= m.Height; y++ {
			id := m.getID(x, y)
			m.Nodes[id] = &Node{ID: id, X: x, Y: y}
		}
	}
	for x := 1; x <= m.Width; x++ {
		for y := 1; y <= m.Height; y++ {
			nextIDs := map[int]struct{}{}
			if x > 1 {
				nextIDs[m.getID(x-1, y)] = struct{}{}
			}
			if x < m.Width {
				nextIDs[m.getID(x+1, y)] = struct{}{}
			}
			if y > 1 {
				nextIDs[m.getID(x, y-1)] = struct{}{}
			}
			if y < m.Height {
				nextIDs[m.getID(x, y+1)] = struct{}{}
			}
			m.Get(x, y).NextIDs = nextIDs
		}
	}
}

func NewMap(w, h int) *Map {
	m := &Map{Width: w, Height: h, Nodes: map[int]*Node{}}
	m.init()
	return m
}

type Searcher struct {
	Map        *Map
	queue      []*Node
	touchedIDs map[int]struct{}
	visitedIDs map[int]struct{}
}

func NewSearcher(m *Map) *Searcher {
	return &Searcher{
		Map:        m,
		queue:      []*Node{},
		touchedIDs: map[int]struct{}{},
		visitedIDs: map[int]struct{}{},
	}
}

func (s *Searcher) Search(start *Node) {
	s.enqueue(start)

	for {
		if len(s.queue) == 0 {
			break
		}
		for nextID := range s.dequeue().NextIDs {
			n := s.Map.GetByID(nextID)
			if n.Color == ColorRed || s.hasTouched(n) {
				continue
			}
			s.enqueue(n)
		}
	}
}

func (s *Searcher) VisitedNodeCount() int {
	return len(s.visitedIDs)
}

func (s *Searcher) hasTouched(n *Node) bool {
	_, ok := s.touchedIDs[n.ID]
	return ok
}

func (s *Searcher) enqueue(n *Node) {
	s.queue = append(s.queue, n)
	s.touchedIDs[n.ID] = struct{}{}
}

func (s *Searcher) dequeue() *Node {
	n := s.queue[0]
	s.queue = s.queue[1:]
	s.visitedIDs[n.ID] = struct{}{}
	return n
}

func main() {
	for sc.Scan() {
		if sc.Text() == "0 0" {
			break
		}
		chunks := strings.Split(sc.Text(), " ")
		w, _ := strconv.Atoi(chunks[0])
		h, _ := strconv.Atoi(chunks[1])

		m := NewMap(w, h)

		// Set colors
		var start *Node
		for y := 1; y <= h; y++ {
			sc.Scan()
			for i, c := range sc.Text() {
				switch c {
				case '.', '@':
					m.SetColor(i+1, y, ColorBlack)
					if c == '@' {
						start = m.Get(i+1, y)
					}
				case '#':
					m.SetColor(i+1, y, ColorRed)
				}
			}
		}

		// Search
		s := NewSearcher(m)
		s.Search(start)
		fmt.Println(s.VisitedNodeCount())
	}
}

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

int array[20][20];
int h, w, sx, sy;
int ans;

void out_array(void);
void input(void);
void search(int, int);

int main(){
	while(true){
		
		cin >> w >> h;
		if(w == 0 && h == 0){
			return 0;
		}

		input();
		ans = 0;
		search(sx, sy);
		cout << ans << endl;

	}
}
void out_array(void){
	for(int i = 0;i < h;i++){
		for(int j = 0;j < w;j++){
			cout << array[i][j];
		}
		cout << endl;
	}
}

void input(void){
	for(int i = 0;i < h;i++){
		for(int j = 0;j < w;j++){
			char c;
			cin >> c;
			
			switch(c){
				case '#':
					array[i][j] = 1;//??????
					break;
					
				case '.':
					array[i][j] = 0;//?????????
					break;
					
				case '@':
					array[i][j] = 0;
					sx = j;//????????????
					sy = i;
			}
		}
	}
}

void search(int x,int y){
	if(array[y][x] == 1 || x >= w || y >= h || x < 0 || y < 0){
		return;
	}else{
		array[y][x] = 1;
		ans++;
	}
	search(x - 1, y);
	search(x + 1, y);
	search(x, y - 1);
	search(x, y + 1);
	return;
}

C++: #include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<cstdlib>
#define cinf(n,x,y) for(int i=0;i<(n);i++) cin >> x[i] >> y[i];
typedef long long int ll;
using namespace std;

int w,h;
string f[20];
int cnt;

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

void dfs(int x,int y){
	f[y][x]='#';
	cnt++;
	for(int i=0;i<4;i++){
		int nx=x+dx[i];
		int ny=y+dy[i];

		if(nx<0||nx>=w)continue;
		if(ny<0||ny>=h)continue;
		if(f[ny][nx]!='.')continue;

		dfs(nx,ny);
	}
}

int main(){
	while(1){
		cin >> w >> h;
		if(w==0&&h==0)break;
		for(int i=0;i<h;i++){
			cin >> f[i];
		}
		cnt=0;
		for(int i=0;i<h;i++){
			for(int j=0;j<w;j++){
				if(f[i][j]=='@')dfs(j,i);
			}
		}
		cout << cnt << endl;
	}
	return 0;
}

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

const int NUM = 7;

void grooping(int y, int x, int w, int h, char** room, unsigned long*** group, unsigned long* next)
{
	if (room[y][x] != '#') {
		for (int i = y - 1; i <= y + 1; i++) {
			for (int j = x - 1; j <= x + 1; j++) {
				if (i < 0 || j < 0 || i >= h || j >= w) {
					continue;
				}
				if ((i == y && j != x) || (i != y && j == x)) {
					for (int k = 0; k < NUM; k++) {
						group[y][x][k] |= group[i][j][k];
					}
				}
			}
		}
		for (int i = 0; i < NUM; i++) {
			if (group[y][x][i] == 0UL && next[i] != 0UL) {
				group[y][x][i] |= next[i];
				next[i] <<= 1;
				break;
			}
		}
	}
}

int main()
{
	int w, h;
	while (true) {
		cin >> w >> h;
		if (w == 0 && h == 0) {
			break;
		}

		unsigned long next[NUM] = { 1UL, 1UL, 1UL, 1UL, 1UL, 1UL, 1UL };
		char** room = new char*[h];
		unsigned long*** group = new unsigned long**[h];
		int x, y;
		for (int i = 0; i < h; i++) {
			room[i] = new char[w];
			group[i] = new unsigned long*[w];
			for (int j = 0; j < w; j++) {
				cin >> room[i][j];
				if (room[i][j] == '@') {
					x = j;
					y = i;
				}
				group[i][j] = new unsigned long[NUM];
				for (int k = 0; k < NUM; k++) {
					group[i][j][k] = 0UL;
				}
			}
		}

		for (int k = 0; k < 2; k++) {
			for (int i = 0; i < h; i++) {
				for (int j = 0; j < w; j++) {
					grooping(i, j, w, h, room, group, next);
				}
			}
			for (int i = h - 1; i >= 0; i--) {
				for (int j = w - 1; j >= 0; j--) {
					grooping(i, j, w, h, room, group, next);
				}
			}
			for (int j = 0; j < w; j++) {
				for (int i = 0; i < h; i++) {
					grooping(i, j, w, h, room, group, next);
				}
			}
			for (int j = w - 1; j >= 0; j--) {
				for (int i = h - 1; i >= 0; i--) {
					grooping(i, j, w, h, room, group, next);
				}
			}
		}

		int count = 0;
		for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++) {
				for (int k = 0; k < NUM; k++) {
					if ((group[i][j][k] & group[y][x][k]) != 0UL) {
						count++;
						break;
					}
				}
			}
		}

		cout << count << '\n';

		for (int i = 0; i < h; i++) {
			delete[] room[i];
			for (int j = 0; j < w; j++) {
				delete[] group[i][j];
			}
			delete[] group[i];
		}
		delete[] room;
		delete[] group;
	}

	return 0;
}

C++: #include<stdio.h>
char a[21][21];
int c;
void dfs(int y,int x){
  c++;
  a[y][x]=0;
  if(y!=0)
    if(a[y-1][x]=='.')
      dfs(y-1,x);
  if(y!=20)
    if(a[y+1][x]=='.')
      dfs(y+1,x);
  if(x!=0)
    if(a[y][x-1]=='.')
      dfs(y,x-1);
  if(x!=20)
    if(a[y][x+1]=='.')
      dfs(y,x+1);
}
int main(){
  int w,h,i,j;
  while(1){
    scanf("%d%d",&w,&h);
    if(w==0&&h==0)break;
    for(i=0;i<21;i++){
      for(j=0;j<21;j++){
	a[i][j]=0;
      }
    }
    for(i=0;i<h;i++){
      for(j=0;j<w;j++){
	scanf("%c",&a[i][j]);
      }
    }
    c=0;
    for(i=0;i<h;i++){
      for(j=0;j<w;j++){
	if(a[i][j]=='@')dfs(i,j);
      }
    }
    printf("%d\n",c);

   
  }
  return 0;
}