Go: package main

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

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

type Color int

const (
	ColorBlack Color = iota
	ColorRed
)

type Node struct {
	ID    int
	X, Y  int
	Color Color
	Nexts []*Node
}

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])

		// Initialize map
		m := map[int]map[int]*Node{}
		for x := 1; x <= w; x++ {
			m[x] = map[int]*Node{}
			for y := 1; y <= h; y++ {
				m[x][y] = &Node{ID: x + y*w, X: x, Y: y}
			}
		}
		for x := 1; x <= w; x++ {
			for y := 1; y <= h; y++ {
				nexts := []*Node{}
				if n, ok := m[x-1][y]; ok {
					nexts = append(nexts, n)
				}
				if n, ok := m[x][y-1]; ok {
					nexts = append(nexts, n)
				}
				if n, ok := m[x+1][y]; ok {
					nexts = append(nexts, n)
				}
				if n, ok := m[x][y+1]; ok {
					nexts = append(nexts, n)
				}
				m[x][y].Nexts = nexts
			}
		}

		// Set colors
		queue := []*Node{}
		touchedIDs := map[int]struct{}{}
		for y := 1; y <= h; y++ {
			sc.Scan()
			for i, c := range sc.Text() {
				switch c {
				case '.', '@':
					n := m[i+1][y]
					n.Color = ColorBlack
					if c == '@' {
						queue = append(queue, n)
						touchedIDs[n.ID] = struct{}{}
					}
				case '#':
					m[i+1][y].Color = ColorRed
				}
			}
		}

		// Search
		visitedIDs := map[int]struct{}{}
		for {
			if len(queue) == 0 {
				break
			}
			n := queue[0]
			queue = queue[1:]
			visitedIDs[n.ID] = struct{}{}
			for _, next := range n.Nexts {
				if next.Color == ColorRed {
					continue
				}
				if _, ok := touchedIDs[next.ID]; !ok {
					queue = append(queue, next)
					touchedIDs[n.ID] = struct{}{}
				}
			}
		}
		fmt.Println(len(visitedIDs))
	}
}

C++: #if 0
08-162015?????????????????°???????????????????????????
pair???
#endif

#include <iostream>
#include <queue>
#include <string.h>
#include <utility>
using namespace std;

int w,h;
int tot=1; //?????£????????????(?????????????????????)
const int dx[]={1,0,-1,0}, dy[]={0,-1,0,1}; //??????????§??????¨
char P[30][30]; //??§?¨?????????????????????¨???

bool valid(int x,int y){ //??????????????????
	return (x>=0)&&(x<w)&&(y>=0)&&(y<h)&&(P[x][y]!='#');
}

void bfs(int x,int y){ //???????????¢?´¢
	queue<pair<int,int> > q;
	pair<int,int> p;
	p = make_pair(x,y); //pair??????????????¨??????????????????
	q.push(p);
	while(!q.empty()){
		pair<int,int> cur=q.front(); //?????¨??°?????????????????????
		q.pop();
		for(int i=0;i<4;++i){
			if(valid(cur.first+dx[i],cur.second+dy[i])){
				tot+=1;
				q.push(make_pair(cur.first+dx[i],cur.second+dy[i]));
				P[cur.first+dx[i]][cur.second+dy[i]]='#'; //???????????£?????´???????°???????
			}
		}
		P[cur.first][cur.second]='#';
	}
	cout << tot <<endl;
}

int main(){
	int x1,y1;
	while((cin>>w>>h)&&(w!=0&&h!=0)){
		for(int i=0;i<h;++i){
			for(int j=0;j<w;++j){
				cin>>P[i][j];
				if(P[i][j]=='@')
					x1=i; y1=j; 
			}
		}
		bfs(x1,y1); //??????????????°????????£??\????????¢?´¢????§?
	}
}

C++: #include <iostream>
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <bitset>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
using namespace std;
typedef long long ll;
typedef pair<int,int> pint;
typedef vector<int> vint;
typedef vector<pint> vpint;
#define mp make_pair
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define REP(i,n) for (int i=(n)-1;i>=0;i--)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define REPS(i,f,n) for (int i=(f)-1;i>=(n);i--)
int dx[4] = {1, 0, 0, -1};
int dy[4] = {0, 1, -1, 0};

char board[21][21];
int w, h;
int x, y;// ?????¨?????????

void slove(void){
	int cnt = 0;
	queue<pint> q;
	q.push(make_pair(y, x));//?????¨????????????queue?????\??????

	while(!q.empty()){
		pint now = q.front(); q.pop();
		rep(i, 4){
			int nowy = now.fi + dy[i];
			int nowx = now.se + dx[i];
			if (0 <= nowy <= h - 1 && 0 <= nowx && nowx <= w - 1){
				if (board[nowy][nowx] == '.'){
					cnt++;
					board[nowy][nowx] = 0;
					q.push(make_pair(nowy, nowx));
				}
			}
		}
	}
	printf("%d\n", cnt + 1);//?§?????????´????????\??????
	return;
}

void scan(int w, int h){
	rep(i, h){
		rep(j, w){
			cin >> board[i][j];
			if (board[i][j] == '@'){
				y = i; x = j;
			}
		}
		getchar();
	}
	
	slove();
	return;
}

int main(void){
	rep(i, 1000){
		cin >> w >> h;

		if (w == 0) break;
		scan(w, h);
	}
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <string>
#include <queue>
using namespace std;
int main() {
  int W, H, x, y, ans, c;
  string s;
  while (cin >> W >> H, W) {
    vector<string> M;
    ans = 0;
    M.push_back(string(W+2, '#'));
    for (int i = 0; i < H; ++i) {
      cin >> s;
      for (int j = 0; j < W; ++j) {
	if (s[j] == '@') {
	  x = i+1;
	  y = j+1;
	  s[j] = '!';
	  break;
	}
      }
      s = '#' + s + '#';
      M.push_back(s);
    }
    M.push_back(string(W+2, '#'));
    queue<vector<int>> que;
    que.push({x, y});
    while (!que.empty()) {
      ++ans;
      x = que.front()[0];
      y = que.front()[1];
      que.pop();
      if (M[x-1][y] == '.') {
	M[x-1][y] = '!';
	que.push({x-1,y});
      }
      if (M[x][y-1] == '.') {
	M[x][y-1] = '!';
	que.push({x,y-1});
      }
      if (M[x+1][y] == '.') {
	M[x+1][y] = '!';
	que.push({x+1,y});
      }
      if (M[x][y+1] == '.') {
	M[x][y+1] = '!';
	que.push({x,y+1});
      }
    }
    cout << ans << endl;
  }
  return 0;
}

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

using namespace std;

char tyle[30][30]={'0'};

int find_tyle(int i,int j){
  if(tyle[i+1][j]=='.'){
    tyle[i+1][j]='a';
    find_tyle(i+1,j);
  }
  if(tyle[i][j+1]=='.'){
    tyle[i][j+1]='a';
    find_tyle(i,j+1);
  }
  if(tyle[i-1][j]=='.'){
    tyle[i-1][j]='a';
    find_tyle(i-1,j);
  }
  if(tyle[i][j-1]=='.'){
    tyle[i][j-1]='a';
    find_tyle(i,j-1);
  }
}

int main(){
  
  int w,h;
  
  while(cin>>w>>h,w){
    int ans=0;
    for(int i=1;i<=h;++i){
      for(int j=1;j<=w;++j){
      cin>>tyle[i][j];
      }
    }
    for(int i=1;i<=h;++i){
      for(int j=1;j<=w;++j){
	if(tyle[i][j]=='@'){
	  find_tyle(i,j);
	  tyle[i][j]='a';
	}
      }
    }
    for(int i=1;i<=h;++i){
      for(int j=1;j<=w;++j){
	if(tyle[i][j]=='a'){
	  ans++;
      }
    }
  }
    cout<<ans<<endl;

   for(int i=0;i<30;++i){
      for(int j=0;j<30;++j){
      tyle[i][j]='0';
      }
    }
    
  }
}

C++: #include <iostream>
#include <queue>

#define MAX_WH 20

typedef std::pair<int, int> P;

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

int W, H, sx, sy;
char field[MAX_WH][MAX_WH];
int solve();

int bfs();

int main(){
	while(true){
		std::cin >> W >> H;
		if(W == 0 && H == 0)
			break;

		for(int i = 0; i < H; ++i){
			for(int j = 0; j < W; ++j){
				char in;
				std::cin >> in;

				if(in == '@')
					sx = j, sy = i;

				field[j][i] = in;
			}
		}

		std::cout << solve() << std::endl;
	}
	return 0;
}

int solve(){
	return bfs();
}

int bfs(){
	std::queue<P> que;
	int ans = 0;
	bool flag[MAX_WH][MAX_WH];

	for(int i = 0; i < MAX_WH; ++i){
		for(int j = 0; j < MAX_WH; ++j)
			flag[i][j] = true;
	}

	que.push(P(sx, sy));
	flag[sx][sy] = false;

	while(!que.empty()){
		++ans;
		P p = que.front(); que.pop();

		for(int i = 0; i < 4; ++i){
			int nx = p.first + dx[i], ny = p.second + dy[i];

			if(nx >= 0 && ny >= 0 && nx < W && ny < H && field[nx][ny] != '#' && flag[nx][ny]){
				flag[nx][ny] = false;
				que.push(P(nx, ny));
			}
		}
	}

	return ans;
}