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 int long long
#define endl '\n'
#define FOR(i, a, n) for (int i = (a); i < (n); ++i)
#define REP(i, n) FOR(i, 0, n)
using namespace std;

const int dy[] = {-1, 0, 0, 1};
const int dx[] = {0, -1, 1, 0};
int w, h;
string s[20];
int sy, sx;

void dfs(int y, int x) {
    s[y][x] = '@';
    REP (i, 4) {
        int ny = y + dy[i];
        int nx = x + dx[i];
        if (ny >= 0 && ny < h && nx >= 0 && nx < w && s[ny][nx] == '.') {
            dfs(ny, nx);
        }
    }
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    while (cin >> w >> h, w) {
        REP (i, h) {
            cin >> s[i];
            REP (j, w) {
                if (s[i][j] == '@') sy = i, sx = j;
            }
        }
        dfs(sy, sx);
        int ans = 0;
        REP (i, h) REP (j, w) ans += (s[i][j] == '@');
        cout << ans << endl;
    }
}

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

int W, H;
char board[30][30];
bool visited[30][30];

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

void dfs(int x, int y) {
   for (int i = 0; i < 4; i++) {
      int nx = x + dx[i], ny = y + dy[i];
      if (nx < 0 || nx >= H || ny < 0 || ny >= W) continue;
      if (board[nx][ny] == '#') continue;
      if (visited[nx][ny]) continue;
      visited[nx][ny] = true;
      dfs(nx, ny);
   }
}

int main() {
   while (cin >> W >> H, W && H) {
      memset(visited, false, sizeof(visited));
      int sx = 0, sy = 0;
      for (int i = 0; i < H; i++) {
         for (int j = 0; j < W; j++) {
            cin >> board[i][j];
            if (board[i][j] == '@') {
               sx = i, sy = j;
            }
         }
      }

      board[sx][sy] = true;
      dfs(sx, sy);

      int cnt = 0;
      for (int i = 0; i < H; i++) {
         for (int j = 0; j < W; j++) {
            if (visited[i][j]) cnt++;
         }
      }

      cout << cnt << endl;
   }

   return 0;
}

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

int main() {
	int w, h, sx, sy;
	while (cin >> w >> h , w != 0 || h != 0) {
		vector<string> field = vector<string>(h);

		for (int i = 0; i < h; i++) {
			cin >> field[i];
		}
		for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++) {
				if (field[i][j] == '@') {
					sx = j;
					sy = i;
				}
			}
		}

		int ans = 0;
		auto visited = vector<vector<bool>>(h, vector<bool>(w, false));
		queue<int> q = queue<int>();
		q.push(sy * 100 + sx);
		while (!q.empty()) {
			int x = q.front() % 100, y = q.front() / 100;
			q.pop();
			if (visited[y][x]) continue;
			ans++;
			visited[y][x] = true;
			int dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};
			for (int i = 0; i < 4; i++) {
				int nx = x + dx[i], ny = y + dy[i];
				if (nx < 0 || w <= nx || ny < 0 || h <= ny) continue;
				if (field[ny][nx] == '.' && !visited[ny][nx])
					q.push(ny * 100 + nx);
			}
		}

		cout << ans << endl;
	}
}

C++: #include <bits/stdc++.h>
#define rep(i,a,b) for(int i=a ; i<b ; i++)
#define dump(x) cout << #x << " = " << x << endl

using namespace std;

int h, w;
char maze[20][20];
int reach[20][20];
pair<int, int> st;

void disp(){
	rep(i,0,h){
		rep(j,0,w) cout << maze[i][j];
		cout << endl;
	}
	cout << endl;

	rep(i,0,h){
		rep(j,0,w) cout << reach[i][j];
		cout << endl;
	}
	cout << endl;
}

int dr[4] = {0, -1, 0, 1};
int dc[4] = {-1, 0, 1, 0};

void dfs(int r, int c){
	if(r<0 or r>h-1 or c<0 or c>w-1) return ;
	if(maze[r][c] == '#' or reach[r][c] == 1) return ;

	reach[r][c] = 1;
	rep(i,0,4){
		dfs(r+dr[i], c+dc[i]);
	}
	return;
}

void solve(){
	int ans=0;

	rep(i,0,h) rep(j,0,w){
		if(reach[i][j] == 1) ans++;
	}
	cout << ans << endl;
	return;
}

int main(){

	while(1){
		cin >> w >> h;
		if(h == 0) break;

		rep(i,0,h) rep(j,0,w){
			cin >> maze[i][j];
			reach[i][j] = 0;
			if(maze[i][j] == '@'){
				st.first = i;
				st.second = j;
			}
		}
		dfs(st.first, st.second);
		solve();
	}


	return 0;
}

C++: #include <iostream>
#include <cmath>
#include <string>
#include <iomanip>
#define GROUND 0
#define WALL 90000
#define INITIAL -1

int count();
void init();
void map();
void mark_n(int,int,int,int,int);
void mark_n_all(int);
bool isValidPoint(int,int);

using namespace std;
const int MAX_W = 20;
const int MAX_H = 20;
char floor_[MAX_W][MAX_H];
//floorツつセツづ算ツ術ツ甘鳴青板づ債ャツつエツづゥ
int step[MAX_W][MAX_H];
int width,height;

int main(){
  //  char floor[MAX_W][MAX_H];
  //int step[MAX_W][MAX_H];
  
  while(cin >> width >> height && width > 0){
    string line;
    int ix,iy;
    //cout << width << " " << height << endl;
    init();
    for(int i = 0; i < height; ++i){
      cin >> line;
      for(int j=0; j < width ; ++j){
	floor_[j][i] = line[j];
	if(line[j]=='@'){
	  step[j][i]=GROUND;
	  ix = j; iy = i;
	}else if(line[j]=='#'){
	  step[j][i]=WALL;
	}
	//cout << step[j][i];
      }
      //cout << endl;
    }
    //cout << count('.') << count('#') << count('@') << endl;
    for(int k = 0; k < 10; k++){
      //map();
      mark_n_all(k);
      //mark_n(k+1,ix,iy,1,0);
      //cout << endl;
      //map();
      
      //cout << endl;
    }
    cout << count() << endl;
  }
  
}

int count(){
  int result =0;
  for(int i=0; i<height;++i){
    for(int j=0; j< width; ++j){
      if(step[j][i] >= 0 && step[j][i] < WALL){
	result++;
      }
    }
  }
  return result;
}

void init(){
  for(int i=0; i<height;++i){
    for(int j=0; j< width; ++j){
      step[j][i]=INITIAL;
    }   
  }
}

void map(){
  for(int i = 0; i < height; ++i){
    for(int j=0; j < width ; ++j){
      cout << setw(5)<< step[j][i] << " ";
    }
    cout << endl;
  }
}

void mark_n(int n,int x,int y,int dx,int dy){
  int temp;
  for(int i =0; i< 4;i++){
    temp = dx;
    dx = dy;
    dy = -temp;
    if(isValidPoint(x+dx,y+dy) && step[x+dx][y+dy]==INITIAL){
      step[x+dx][y+dy] = n;
    }
  }
}


void mark_n_all(int n){
  for(int i = 0; i < height; i++){
    for(int j = 0; j < width ; j++){
      if(step[j][i]==n){
	//	cout << j <<" " << i << "jツづツづ個値"<< endl;
	mark_n(n+1,j,i,1,0);
      }
    }
  }
}



bool isValidPoint(int x,int y){
  if(x < 0 || x >  width || y < 0 || y > height){
    return false;
  }else{
    return true;
  }
}