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 <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <ctime>
#include <cassert>
#include <iostream>
#include <cctype>
#include <sstream>
#include <string>
#include <list>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <map>
#include <utility>
#include <numeric>
#include <algorithm>
#include <iterator>
#include <bitset>
#include <complex>
#include <fstream>
using namespace std;
typedef long long ll;
const double EPS = 1e-9;
typedef vector<int> vint;
typedef pair<int, int> pint;
#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for(int i = x; i < n; i++)
template<class T> T RoundOff(T a){ return int(a+.5-(a<0)); }
template<class T, class C> void chmax(T& a, C b){ if(a < b) a = b; }
template<class T, class C> void chmin(T& a, C b){ if(b < a) a = b; }
template<class T, class C> pair<T, C> mp(T a, C b){ return make_pair(a, b); }

struct P{ P(int x, int y) : x(x), y(y) {} double x, y; };

int main()
{
    int w, h;
    while(cin >> w >> h && w)
    {
        vector<vector<char> > m(h, vector<char>(w));
        P s(0, 0);
        
        rep(y, h) rep(x, w)
        {
            cin >> m[y][x];
            if(m[y][x] == '@')
                s = P(x, y);
        }
        
        int res = 1;
        queue<P> que;
        for(que.push(s); !que.empty(); que.pop())
        {
            P p = que.front();
            
            int dx[] = {1, -1, 0, 0}, dy[] = {0, 0, 1, -1};
            rep(i, 4)
            {
                int nx = p.x + dx[i], ny = p.y + dy[i];
                
                if(0 <= nx && nx < w && 0 <= ny && ny < h && m[ny][nx] == '.')
                {
                    m[ny][nx] = '#';
                    res++;
                    
                    que.push(P(nx, ny));
                }
            }
        }
        
        cout << res << endl;
    }
}

C++: #include <iostream>
#include <queue>
#include <cstdio>	
#define rep(i,n) for(int i=0;i<(n);i++)

using namespace std;

typedef pair<int, int> P;
char tile[25][25];

int main()
{
	const int dir[][2] = { {-1, 0 }, { 0, 1 }, { 1, 0 }, { 0, -1 } };
	int w, h;
	while (scanf ("%d %d", &w, &h ) && w && h ){
		P s = P (-1, -1 );
		rep (i, h ){
			rep (j, w ){
				scanf (" %c", tile[i]+j );
				if (tile[i][j] == '@' ){
					s.first = i, s.second = j;
				} // end if
			} // end rep
		} // end rep
		queue<P> que;
		que.push (s );
		while (!que.empty() ){
			P curr = que.front(); que.pop();
			int row = curr.first;
			int col = curr.second;
			rep (k, 4 ){
				int nr = row + dir[k][0];
				int nc = col + dir[k][1];
				if (nr < 0 || nc < 0 || nr >= h || nc >= w || tile[nr][nc] == '#' || tile[nr][nc] == '@' ) continue;
				que.push (P (nr, nc ) );
				tile[nr][nc] = '@';
			} // end rep
		} // end while
		int res = 0;
		rep (i, h ){
			rep (j, w ){
				if (tile[i][j] == '@' ) res++;
			} // end rep
		} // end rep
		printf ("%d\n", res );
	} // end while

	return 0;
}

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

char field[30][30];
int res;
int w, h;
constexpr int dd[] = {0, 1, 0, -1, 0};

void dfs(int y, int x) {
  res++;
  field[y][x] = 'x';
  for (int i = 0; i < 4; ++i) {
    int ny = dd[i] + y, nx = dd[i + 1] + x;
    if (0 <= ny && ny < h && 0 <= nx && nx < w) {
      if (field[ny][nx] == '.') {
        dfs(ny, nx);
      }
    }
  }
}

int main() {
  while (cin >> w >> h, w || h) {
    int sy, sx;
    for (int i = 0; i < h; ++i) {
      for (int j = 0; j < w; ++j) {
        cin >> field[i][j];
        if (field[i][j] == '@') {
          sy = i;
          sx = j;
          field[i][j] = '.';
        }
      }
    }
    res = 0;
    dfs(sy, sx);
    cout << res << endl;
  }
}

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 < 50; 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;
}