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>
using namespace std;
#define rep(i,n) for (int (i)=(0);(i)<(int)(n);++(i))
using ll = long long;
using P = pair<int, int>;
using namespace std;

template<class T> void vin(vector<T>& v, int n) {
    v.resize(n);
    for (int i = 0; i < n; ++i) {
        cin >> v[i];
    }
}

int w, h;
char ch[50][50];
int dx[] = { 0, 1, 0, -1 };
int dy[] = { 1, 0, -1, 0 };

void bfs(int y, int x) {
    rep(i, 4) {
        int ny = y + dy[i], nx = x + dx[i];
        if (0 > ny or 0 > nx or ny >= h or nx >= w) continue;
        if (ch[ny][nx] == '.') {
            ch[ny][nx] = 'a';
        }
    }
}

int main() {
    while (cin >> w >> h and w and h) {
        int py = 0, px = 0;
        rep(i, h) rep(j, w) {
            cin >> ch[i][j];
            if (ch[i][j] == '@') {
                py = i, px = j;
                ch[i][j] = '.';
            }
        }
        bfs(py, px);
        int ans = 0;
        rep(i, h) rep(j, w) if (ch[i][j] == 'a') ans++;
        cout << ans << endl;
    }
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef vector<string> V;
typedef pair<int, int> P;
typedef queue<P> Q;
int main() {
	int w, h, x, y;
	cin >> w >> h;
	if (w == 0 && h == 0) {
		return 0;
	}
	V map = V(h);
	for (int i = 0; i < h; i++) {
		cin >> map[i];
		for (int j = 0; j < w; j++) {
			if (map[i][j] == '@') {
				x = j;
				y = i;
			}
		}
	}
	int n = 0;
	Q q;
	q.push(P(y, x));
	while (q.size()) {
		P p = q.front();
		q.pop();
		if (p.first < 0 || h <= p.first || p.second < 0 || w <= p.second || map[p.first][p.second] == '#') {
			continue;
		}
		//cout << p.second << " " << p.first << " " << map[p.first][p.second] <<endl;
		map[p.first][p.second] = '#';
		n++;
		q.push(P(p.first - 1, p.second));
		q.push(P(p.first + 1, p.second));
		q.push(P(p.first, p.second - 1));
		q.push(P(p.first, p.second + 1));
	}
	cout << n << endl;
	return main();
}

C++: #include <iostream>

using namespace std;

const int dx[]={1,0,-1,0}, dy[]={0,-1,0,1};
int H,W,count=0;
char **map;
bool **isCount;

bool valid(int x,int y)
{
    return x<=(W-1)&&x>=0&&y<=(H-1)&&y>=0;
}

void bfs(int x,int y)
{
    if(valid(x,y)&&map[y][x]!='#' && !isCount[y][x])
    {
        count++;
        isCount[y][x]=true;
        for(int i=0;i<4;i++)
            bfs(x+dx[i],y+dy[i]);
    }
  /*int D[100];
  for(int i=0;i<100;i++)
    D[i]=-1;
  queue<int>Q;
  Q.push(src);
  D[src]=0;
  while(!Q.empty())
    {
      int cur=Q.front();
      Q.pop();
       for(int dst=0;dst<n;dst++)
	{
	  if(M[cur][dst]==1&&D[dst]==-1)
	    {
	      D[dst]=D[cur]+1;
	      Q.push(dst);
	    }
    }
    }
    for(int i=0;i<n;i++)
        cout<<i+1<<' '<<D[i]<<endl;
        */
}



int main()
{
    int x,y;
    cin>>W>>H;
    while(W!=0&&H!=0)
    {
        isCount=new bool*[H];
        map=new char*[H];
        for(int i=0;i<H;i++)
        {
            isCount[i]=new bool[W];
            map[i]=new char[W];
        }
        for(int i=0;i<H;i++)
        {
            for(int j=0;j<W;j++)
                isCount[i][j]=false;
        }
        for(int i=0;i<H;i++)
        {
            for(int j=0;j<W;j++)
            {
                cin>>map[i][j];
                if(map[i][j]=='@')
                {
                    x=j;
                    y=i;
                }
            }
        }
        bfs(x,y);
        cout << count << endl;
        delete map;
        delete isCount;
        cin>>W>>H;
        count=0;
    }
    return 0;
}

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

using namespace std;

#define rep(i, n) for(int i=0; i<(n); ++i)
const int dx[] = {-1, 0, 1, 0}, dy[] = {0, -1, 0, 1};

int W, H;

inline bool inrect(int x, int y){
    return 0 <= x && x < H && 0 <= y && y < W;
}

int dfs(vector<string>& room, int x, int y){
    room[x][y] = '#';
    int res = 1;
    rep(i, 4){
        int nx = x + dx[i], ny = y + dy[i];
        if(!inrect(nx, ny) || room[nx][ny] == '#')continue;
        res += dfs(room, nx, ny);
    }
    return res;
}

int main(){
    while(cin >> W >> H, W|H){
        vector<string> room(H);
        int sx = -1, sy = -1;
        rep(i, H){
            cin >> room[i];
            rep(j, W)if(room[i][j] == '@')sx = i, sy = j;
        }
        cout << dfs(room, sx, sy) << '\n';
    }
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

int w,h;
string g[100];
const int dy[] = {-1,0,1,0}, dx[] = {0,1,0,-1};

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

  int res = 1;
  for(int i=0;i<4;i++){
    int ny = y+dy[i], nx = x+dx[i];
    if(ny<0 || nx<0 || ny>=h || nx>=w)continue;
    if(g[ny][nx] == '.')res += dfs(ny,nx);
  }
  return res;
}

int main(){
  while(cin >> w >> h, w){
    for(int i=0;i<h;i++)cin >> g[i];

    for(int i=0;i<h;i++){
      for(int j=0;j<w;j++){
	if(g[i][j] == '@')cout << dfs(i,j) << endl;
      }
    }
  }
}

C++: #include <iostream>
using namespace std;
int a=0;
int box[20][20];
int  kazoe(int p,int P,int H,int W){
  int i,I;
  a++;
  box[p][P]=0;
  if(box[p][P+1]==1) kazoe(p,P+1,H,W);
  if(box[p][P-1]==1) kazoe(p,P-1,H,W);
  if(box[p-1][P]==1) kazoe(p-1,P,H,W);
  if(box[p+1][P]==1) kazoe(p+1,P,H,W);
  else {
  return a;
  }
}
int main(){
  int i,I,H,W,p,P;
  
  char v;
  while(1){
  cin>>W>>H;
  if(W==0&&H==0) break;
  for(i=0;i<H;i++){
    for(I=0;I<W;I++){
      cin>>v;
      if(v=='.') box[i][I]=1;
      if(v=='#') box[i][I]=2;
      if(v=='@') {
	box[i][I]=0;
	p=i;
	P=I;
      }
    }
  }
  cout<<kazoe(p,P,H,W)<<endl;
  a=0;
  for(i=0;i<H;i++){
    for(I=0;I<W;I++){
      box[i][I]=0;
    }
  }
  
 
  }
  return 0;
}