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 = 0;
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) {
		rep(i, H) cin >> field[i];
		rep(i, H) rep(j, W) {
			if (s[i][j] == '@') solve(i, j);
		}
	}
	return 0;
}

C++: #include<iostream>
using namespace std;
#define r(i,n) for(int i=0;i<n;i++)
int ans=1,n,m;
char map[30][30];

void d(int x,int y){
  if(x==m||y==n||x<0||y<0)return;
  if(map[x][y]=='.')ans++;
  if(map[x][y]=='#')return;
  map[x][y]='#';
  d(x+1,y),d(x-1,y),d(x,y+1),d(x,y-1);
}

int main(){
  while(cin>>n>>m,n){
  int x,y;
  ans=1;
  r(i,m)r(j,n){
    cin>>map[i][j];
    if(map[i][j]=='@')x=i,y=j;
  }
  d(x,y);
  cout<<ans<<endl;
  }
  return 0;
}

C++: #include<stdio.h>
#include<iostream>
#include<algorithm>

using namespace std;

char tile[30][30];
int W, H;
int ix, iy;
int cnt;
int dx[4] = { 1, 0, -1, 0 };
int dy[4] = { 0, 1, 0, -1 };

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

	cnt++;

	for (int i = 0; i < 4; i++)
	{
		int X = x + dx[i];
		int Y = y + dy[i];
		if (0 <= X&&X < W && 0 <= Y&&Y < H&&tile[Y][X] != '#')
		{
			dfs(X,Y);
		}
	}
}

int main()
{
	while (cin >> W >> H, W + H != 0)
	{
		for (int y = 0; y < H; y++)
		{
			for (int x = 0; x < W; x++)
			{
				cin >> tile[y][x];

				if (tile[y][x]=='@')
				{
					ix = x;
					iy = y;
				}
			}
		}

		dfs(ix,iy);
		
		cout << cnt << endl;

		cnt = 0;
	
	
	}

	return 0;
}

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

int vis[25][25];

void inti(){
  for(int i=0;i<25;i++){
    for(int j=0;j<25;j++){
      vis[i][j]=0;
    }
  }
}

void dfs(int i,int j){
  if(vis[i][j]==0 || vis[i][j]==2)return;
  vis[i][j]=0;

    dfs(i-1,j);
    dfs(i,j-1);
    dfs(i,j+1);
    dfs(i+1,j);
}

int main(){
  int w,h;
  int i,j;
  char ch;
  int cnt;

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

    for(i=1;i<=h;i++){
      for(j=1;j<=w;j++){
	cin >> ch;
	if(ch=='.'){
	  vis[i][j]=1;
	}else if(ch=='#'){
	  vis[i][j]=2;
	}else{
	  vis[i][j]=5;
	}
      }
    }
     for(i=1;i<=h;i++){
      for(j=1;j<=w;j++){
	if(vis[i][j]==5)dfs(i,j);
      }
     }
      for(i=1;i<=h;i++){
      for(j=1;j<=w;j++){
	if(vis[i][j]==0)cnt++;
      }
     }
      cout << cnt << endl;
  }
}

C++: #include<bits/stdc++.h>
using namespace std;
int main(){
  int w,h,a[21][21],count=0,m;
  char in;
  while(1){
    cin>>w>>h;
    if(w==0 && h==0) break;
    for(int i=0;i<h;i++){
      for(int j=0;j<w;j++){
	cin>>in;
	if(in=='#') a[i][j]=0;
	else if(in=='@') {
	  a[i][j]=2;
	}
	else a[i][j]=1;
      }
    }
    count=0;
    while(1){
      m=0;
      for(int i=0;i<h;i++){
	for(int j=0;j<w;j++){
	  if(a[i][j]==2){
	    m=1;
	    count++;
	    a[i][j]=3;
	    if(i==0){
	      if(j==0){
		if(a[i+1][j]==1) a[i+1][j]=2;
		if(a[i][j+1]==1) a[i][j+1]=2;
	      }
	      else {
		if(a[i][j-1]==1) a[i][j-1]=2;
		if(a[i+1][j]==1) a[i+1][j]=2;
		if(a[i][j+1]==1) a[i][j+1]=2;
	      }
	    }
	    else if(j==0){
		if(a[i-1][j]==1) a[i-1][j]=2;
		if(a[i+1][j]==1) a[i+1][j]=2;
		if(a[i][j+1]==1) a[i][j+1]=2;
	    }
	    else if(i==h-1){
	      if(j==w-1){
		if(a[i-1][j]==1) a[i-1][j]=2;
		if(a[i][j-1]==1) a[i][j-1]=2;
	      }
	      else {
		if(a[i][j+1]==1) a[i][j+1]=2;
		if(a[i-1][j]==1) a[i-1][j]=2;
		if(a[i][j-1]==1) a[i][j-1]=2;
	      }
	    }
	    else if(j==w-1){
		if(a[i+1][j]==1) a[i+1][j]=2;
		if(a[i-1][j]==1) a[i-1][j]=2;
		if(a[i][j-1]==1) a[i][j-1]=2;
	    }
	    else {
		if(a[i+1][j]==1) a[i+1][j]=2;
		if(a[i-1][j]==1) a[i-1][j]=2;
		if(a[i][j-1]==1) a[i][j-1]=2;
		if(a[i][j+1]==1) a[i][j+1]=2;
	    }
	  }
	}
      }
      if(m==0) break;
      
    }
    cout<<count<<endl;
  }
    
    
  return 0;
}

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

using namespace std;
typedef pair<int,int> pos;

void sub(int x,int y,vector<string> &field,
		vector<pos> &next,int &count){

	if(x>=0 && x<field[0].size() &&
			y>=0 && y<field.size()
			&& field[y][x]=='.'){
				field[y][x]='#';
				count++;
				next.push_back(make_pair(x,y));
			}
}

int solve(int px,int py,vector<string> field){
	int count=1;
	vector<pos> p;
	p.push_back(make_pair(px,py));
	
	field[py][px]='#';
	while(!p.empty()){
		vector<pos> next;
		for(int i=0;i<p.size();i++){
			int x = p[i].first;
			int y = p[i].second;
			sub(x-1,y,field,next,count);
			sub(x,y-1,field,next,count);
			sub(x+1,y,field,next,count);
			sub(x,y+1,field,next,count);
		}
		p=next;
	}
	return count;
}

int main(){
	while(true){
		int sx,sy;
		cin >> sx >> sy;
		if(sx==0 && sy==0)return 0;
		vector<string> field;
		int x,y;
		for(int i=0;i<sy;i++){
			string str;
			for(int k=0;k<sx;k++){
				char c;
				cin>>c;
				if(c!='.' && c!='#' && c!='@'){cout <<"error"<<endl;}
				str.push_back(c);
				if(c=='@'){
					x=k;
					y=i;
				}
			}
			field.push_back(str);
		}
		cout << solve(x,y,field) << endl;
	}
}