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<bits/stdc++.h>
#define INF 2000000000
#define MOD 1000000007
#define EPS (1e-10)

using namespace std;


vector<int>  dx = {1,-1,0,0};
vector<int>  dy = {0,0,1,-1};

int ans = 0;
int W,H;

bool in_range(int x,int y) {
	if (0 <= x and x < W and 0 <= y and y < H) {
		return true;
	}else {
		return false;
	}
}
int dfs(vector<string> &tab,int x, int y) {
	int ret = 0;
	if (tab[y][x] == '#' or tab[y][x] == '/') return  0;
	if (tab[y][x] == '.') {
		ret += 1;
		tab[y][x] = '/';
	}

	for (int i = 0; i < 4; i++) {
		int nx = x + dx[i];
		int ny = y + dy[i];
		if (in_range(nx,ny)) {
			ret += dfs(tab,nx,ny);	
		}
	}
	return ret;
}

void printv(vector<string> v){
	for(int i = 0; i < v.size(); i++){
		cout << v[i] << endl;
	}
}

int main() {
	
	while(1) {
		cin >> W >> H;
		if (W + H == 0) break;
		int x,y;
		vector<string> tab;
		for (int i = 0; i < H; i++) {
			string s; cin >> s;
			tab.push_back(s);
		}
		for (int i = 0; i < H; i++) {
			for (int j = 0; j < W; j++) {
				if (tab[i][j] == '@') {
					x = j;
					y = i;
				}
			}
		}
		//printv(tab);
		cout << dfs(tab,x,y) + 1 << endl;
		//printv(tab);
	}

	return 0;
}

C++: #include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < (int)n; ++i)
#define REP(i, a, b) for (int i = (int)a; i < (int)b; ++i)
#define rer(i, a, b) for (int i = (int)a; i <= (int)b; ++i)
#define each(i,c) for(__typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define all(v) v.begin(), v.end()
#define mset(a, n) memset(a, n, sizeof(a))

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<vector<int> > vvi;
typedef vector<pair<int, int> > vpii;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;

const int inf = 1000000000;
const int mod = 1000000007;
const double eps = 1e-9;
const int dx[] = { -1, 0, 1, 0};
const int dy[] = { 0, -1, 0, 1};

int W, H;
int ans = 0;
string field[100];

void dfs(int y, int x) {
	if (x < 0 || y < 0 || x == W || y == H) return;
	if (field[y][x] == '#') return;
	ans++;
	field[y][x] = '#';
	rep(i, 4) dfs(y + dy[i], x + dx[i]);
}

int main() {
	while (cin >> W >> H, W) {
		rep(i, H) cin >> field[i];
		rep(i, H) rep(j, W) {
			if (s[i][j] == '@') solve(i, j);
		}
	}
	return 0;
}

C++: #include<iostream>
using namespace std;
#define r(i,n) for(int i=0;i<n;i++)
int ans=1,n,m;
char map[30][30];

void d(int x,int y){
  if(x==m||y==n||x<0||y<0)return;
  if(map[x][y]=='.')ans++;
  if(map[x][y]=='#')return;
  map[x][y]='#';
  d(x+1,y),d(x-1,y),d(x,y+1),d(x,y-1);
}

int main(){
  while(cin>>n>>m,n){
  int x,y;
  ans=1;
  r(i,m)r(j,n){
    cin>>map[i][j];
    if(map[i][j]=='@')x=i,y=j;
  }
  d(x,y);
  cout<<ans<<endl;
  }
  return 0;
}

C++: #include<stdio.h>
#include<iostream>
#include<algorithm>

using namespace std;

char tile[30][30];
int W, H;
int ix, iy;
int cnt;
int dx[4] = { 1, 0, -1, 0 };
int dy[4] = { 0, 1, 0, -1 };

void dfs(int x, int y)
{
	tile[y][x] = '#';

	cnt++;

	for (int i = 0; i < 4; i++)
	{
		int X = x + dx[i];
		int Y = y + dy[i];
		if (0 <= X&&X < W && 0 <= Y&&Y < H&&tile[Y][X] != '#')
		{
			dfs(X,Y);
		}
	}
}

int main()
{
	while (cin >> W >> H, W + H != 0)
	{
		for (int y = 0; y < H; y++)
		{
			for (int x = 0; x < W; x++)
			{
				cin >> tile[y][x];

				if (tile[y][x]=='@')
				{
					ix = x;
					iy = y;
				}
			}
		}

		dfs(ix,iy);
		
		cout << cnt << endl;

		cnt = 0;
	
	
	}

	return 0;
}

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

int vis[25][25];

void inti(){
  for(int i=0;i<25;i++){
    for(int j=0;j<25;j++){
      vis[i][j]=0;
    }
  }
}

void dfs(int i,int j){
  if(vis[i][j]==0 || vis[i][j]==2)return;
  vis[i][j]=0;

    dfs(i-1,j);
    dfs(i,j-1);
    dfs(i,j+1);
    dfs(i+1,j);
}

int main(){
  int w,h;
  int i,j;
  char ch;
  int cnt;

  while(1){
    inti();
    cnt=0;
    cin >> w >> h;
    if(w==0 && h==0)break;

    for(i=1;i<=h;i++){
      for(j=1;j<=w;j++){
	cin >> ch;
	if(ch=='.'){
	  vis[i][j]=1;
	}else if(ch=='#'){
	  vis[i][j]=2;
	}else{
	  vis[i][j]=5;
	}
      }
    }
     for(i=1;i<=h;i++){
      for(j=1;j<=w;j++){
	if(vis[i][j]==5)dfs(i,j);
      }
     }
      for(i=1;i<=h;i++){
      for(j=1;j<=w;j++){
	if(vis[i][j]==0)cnt++;
      }
     }
      cout << cnt << endl;
  }
}