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++: #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;
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) {
		ans = 0;
		rep(i, H) cin >> field[i];
		rep(i, H) rep(j, W) {
			if (field[i][j] == '@') dfs(i, j);
		}
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define FOR(i,k,n) for(int i = (int)(k); i < (int)(n); i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(a) a.begin(), a.end()
#define MS(m,v) memset(m,v,sizeof(m))
#define D10 fixed<<setprecision(10)
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<string> vs;
typedef pair<int, int> pii;
const int MOD = 1000000007;
const int INF = MOD + 1;
const ld EPS = 1e-12;
template<class T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template<class T> T &chmax(T &a, const T &b) { return a = max(a, b); }

/*--------------------template--------------------*/
const int dx[] = { -1, 0, 0, 1 }, dy[] = { 0, -1, 1, 0 };
//[const int dx[] = { -1, -1, -1, 0, 0, 1, 1, 1 }, dy[] = { 0, -1, 1, -1, 1, 0, -1, 1 };
bool valid(int x, int y, int h, int w) { return (x >= 0 && y >= 0 && x < h&&y < w); }
int place(int x, int y, int w) { return w*x + y; }

struct UnionFind
{
	vector<int> par;
	UnionFind(int n) :par(n, -1) {}
	int find(int x) { return par[x] < 0 ? x : par[x] = find(par[x]); }
	void unite(int x, int y)
	{
		x = find(x); y = find(y);
		if (x == y) return;
		if (par[y] < par[x]) swap(x, y);
		if (par[x] == par[y]) par[x]--;
		par[y] = x;
		if (find(x) != find(y)) par[find(y)] = x;
	}
	int count()
	{
		int cnt = 0;
		REP(i, par.size()) if (par[i] < 0) cnt++;
		return cnt;
	}
	bool same(int x, int y)
	{
		return find(x) == find(y);
	}
};


int main()
{
	cin.sync_with_stdio(false);
	int h, w;
	while (cin >> w >> h, h)
	{
		vs fld(h);
		REP(i, h) cin >> fld[i];
		int st;
		REP(i, h)REP(j, w)
		{
			if (fld[i][j] == '@')
			{
				st = place(i, j, w);
				fld[i][j] = '.';
			}
		}
		UnionFind uf(h*w);
		REP(i, h)REP(j, w)
		{
			if (fld[i][j] == '#') continue;
			REP(k, 4)
			{
				int nx = i + dx[k], ny = j + dy[k];
				if (!valid(nx, ny, h, w) || fld[nx][ny] == '#') continue;
				uf.unite(place(i, j, w), place(nx, ny, w));
			}
		}
		int cnt = 0;
		REP(i, h*w)
		{
			if (uf.same(i, st)) cnt++;
		}
		cout << cnt << 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<bits/stdc++.h>
using namespace std;

struct Node{
    int x, y;
};

int dx[4] = {0,1,0,-1}, dy[4] = {-1,0,1,0};
char room[25][25];

int main(){
    int w, h;
    while(cin >> w >> h, w != 0){
        for(int i=0;i<=h+1;++i){
            for(int j=0;j<=w+1;++j){
                if(i == 0 || j == 0 || i == h+1 || j == w+1)
                    room[i][j] = '#';
                else
                    room[i][j] = '.';
            }
        }
        int sx = 0, sy = 0;
        for(int i=0;i<h;++i){
            for(int j=0;j<w;++j){
                scanf(" %c",&room[i+1][j+1]);
                if(room[i+1][j+1] == '@'){
                    sx = j+1;
                    sy = i+1;
                }
            }
        }
        queue<Node> que;
        que.push((Node){sx, sy});
        while(!que.empty()){
            Node curr = que.front(); que.pop();
            for(int i=0;i<4;++i){
                int nx = curr.x + dx[i], ny = curr.y + dy[i];
                if(room[ny][nx] == '.'){
                    room[ny][nx] = '@';
                    que.push((Node){nx, ny});
                }
            }
        }
        int ans = 0;
        for(int i=1;i<=h;++i)
            for(int j=1;j<=w;++j)
                if(room[i][j] == '@')ans++;
        cout << ans << endl;
    }

    return 0;
}