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>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <algorithm>
#include <cmath>
#include <string>

using namespace std;

typedef vector <int> VI;
typedef vector <VI> VVI;
typedef vector <string> VS;
typedef pair<int,int> PII;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair <int, LL> PIL;
typedef vector <PIL> VPIL;


#define each(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); i++)
#define sort(c) sort((c).begin(),(c).end())

#define range(i,a,b) for(int i=(a); i < (b); i++)
#define rep(i,n) range(i,0,n)

#define MAX_INT 2147483647

int dx[] = {1,0,-1,0};
int dy[] = {0,1,0,-1};
int result; 
string field[20];
void dfs(int hx, int hy, int Lx, int Ly, int Ux, int Uy){
	int nx, ny;
	if(field[hy][hx] != '#'){
		result++;
		field[hy][hx] = '#';
		rep(i,4){
			nx = hx + dx[i]; ny = hy + dy[i];
			if (Lx <= nx && nx < Ux && Ly <= ny && ny < Uy) 
				dfs(nx, ny, Lx, Ly, Ux, Uy);
		}
	}
}
int main(){
	int W, H;
	while (1){
		cin >> W >> H;
		if (!(W and H)) break;
		result = 0;
		rep(i,H) cin >> field[i];
		rep(i,H) rep(j,W) if (field[i][j] == '@') dfs(j,i,0,0,W,H);
				cout << result << endl; 
	}
	return 0;
}

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

const int MAX_SIZE = 21;
typedef pair<int, int> P;

int calc(char f[][MAX_SIZE], queue<P> q, int W, int H) {
  int n = 0;
  while (q.size()) {
    n++;
    P p = q.front();
    q.pop();
    int di[] = {-1, 1, 0, 0};
    int dj[] = {0, 0, -1, 1};
    for (int k = 0; k < 4; ++k) {
      int i = p.first  + di[k];
      int j = p.second + dj[k];
      if (i >= 0 && j >= 0 && i < H && j < W && f[i][j] == '.') {
        f[i][j] = '#';
        q.push(P(i, j));
      }
    }
  }
  return n;
}
int main() {
  int W, H;
  char f[MAX_SIZE][MAX_SIZE];
  while (true) {
    queue<P> q;
    cin >> W >> H;
    if (W == 0 && H == 0) break;
    for (int i = 0; i < H; ++i) {
      cin >> f[i];
      for (int j = 0; j < W; ++j) {
        if (f[i][j] == '@') {
          q.push(P(i, j));
        }
      }
    }
    cout << calc(f, q, W, H) << endl;
  }
}

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

int main() {
	int W,H,result,up;
	char c;
	int a[22][22];
	while(1){
		for(int i = 0;i <= 21;i++){
			for(int j = 0;j <= 21;j++){
				a[i][j] = 0;
			}
		}
		result = 1;
		cin >> W >> H;
		if(W == 0)break;
		for(int i = 1;i <= H;i++){
			for(int j = 1;j <= W;j++){
				cin >> c;
				if(c == '.')a[i][j] = 1;
				else if(c == '@')a[i][j] = 2;
			}
		}
		while(1){
			up = 0;
		for(int i = 1;i <= H;i++){
			for(int j = 1;j <= W;j++){
				if(a[i][j] == 2 && a[i-1][j] == 1){
					a[i-1][j] = 2;
					up++;
				}
				if(a[i][j] == 2 && a[i][j-1] == 1){
					a[i][j-1] = 2;
					up++;
				}
				if(a[i][j] == 2 && a[i+1][j] == 1){
					a[i+1][j] = 2;
					up++;
				}
				if(a[i][j] == 2 && a[i][j+1] == 1){
					a[i][j+1] = 2;
					up++;
				}
			}
		}
		result += up;
		if(up == 0)break;	
		}
	cout << result <<endl;
	}
	return 0;
}

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

using namespace std;


int frip(vector<vector<char>>& map, int h, int w, int H, int W)
{
    int cnt = (map[h][w] == '.') ? 1 : 0;
    map[h][w] = 'x';
    if(w != 0 && map[h][w-1] == '.'){
        //++cnt;
//        map[h-1][w-1] = 'x';
        cnt += frip(map, h, w-1, H, W);
    }
    if(w != W-1 && map[h][w+1] == '.'){
        //++cnt;
//        map[h-1][w+1] = 'x';
        cnt += frip(map, h, w+1, H, W);
    }
    if(h != H-1 && map[h+1][w] == '.'){
        //++cnt;
//        map[h+1][w-1] = 'x';
        cnt += frip(map, h+1, w, H, W);
    }
    if(h != 0 && map[h-1][w] == '.'){
        //++cnt;
//        map[h+1][w+1] = 'x';
        cnt += frip(map, h-1, w, H, W);
    }
    
    return cnt;
}


int solve(vector<vector<char>>& map, int H, int W)
{
    int ci, cj;
    for(int i=0;i<H;++i) for(int j=0;j<W;++j) if(map[i][j] == '@') { ci = i; cj = j; }
    
    return frip(map, ci, cj, H, W) + 1;
}


int main()
{
    int H, W;
    while(cin >> W >> H, H){
        vector<vector<char>> map(H);
        for(int i=0;i<H;++i){
            string str{};
            cin >> str;
            map[i] = vector<char>(str.begin(), str.end());
        }
        
        cout << solve(map, H, W) << endl;
//        for(int i=0;i<H;++i){
//            for(int j=0;j<W;++j) cout << map[i][j];
//            cout << endl;
//        }
    }
    
    return 0;
}