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<iostream>
#include<cstdio>
#include<vector>

using namespace std;

int w,h;
int ans=1;
char tile[21][21];

void saiki(int x,int y){
	if(x<0 | x>h | y<0 | y>w)return;
	tile[x][y]='#';
	if(tile[x-1][y]=='.')ans++,saiki(x-1,y);
	if(tile[x+1][y]=='.')ans++,saiki(x+1,y);
	if(tile[x][y-1]=='.')ans++,saiki(x,y-1);
	if(tile[x][y+1]=='.')ans++,saiki(x,y+1);
}

int main(void){
	int a,b; 
	while(1){
		scanf("%d %d",&w,&h);
		if(w==0 && h==0)break;
		ans=1;
		for(a=0;a<h;a++){
			scanf("%s",tile[a]);
		}
		for(a=0;a<h;a++){
			for(b=0;b<w;b++){
				if(tile[a][b]=='@')saiki(a,b);
			}
		}
		printf("%d\n",ans);
	}
	return 0;
}

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

using namespace std;

int w, h;
int mx[] = {0, 0, -1, 1};
int my[] = {-1, 1, 0, 0};

int dfs(int x, int y, vector<string> &v) {
    int cnt = 1;
    for ( int i = 0; i < 4; i++ ) {
        int nx = x + mx[i], ny = y + my[i];
        if ( 0 <= nx && nx < w && 0 <= ny && ny < h && v[ny][nx] == '.' ) {
            v[ny][nx] = '#';
            cnt += dfs(nx, ny, v);
        }
    }
    return cnt;
}

int main() {
    while ( true ) {
        int x, y;
        cin >> w >> h;
        if ( w == 0 && h == 0 ) break;

        vector<string> v(h);

        for ( int i = 0; i < h; i++ ) {
            cin >> v[i];

            for ( int j = 0; j < v[i].size(); j++ ) {
                if ( v[i][j] == '@' ) {
                    y = i;
                    x = j;
                }
            }
        }

        cout << dfs(x, y, v) << endl;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
#define REP(i,a) for(int i=0;i<(a);i++)
#define MOD 1000000007

int main(){
  while(1){
    int h,w;
    cin>>w>>h;
    if(h==0&&w==0) break;
    char a[h][w];
    queue<pair<int,int>> q;
    bool used[h][w];
    for(int i=0;i<h;i++){
      for(int j=0;j<w;j++){
        cin>>a[i][j];
        used[i][j]=0;
        if(a[i][j]=='@') q.push(make_pair(i,j));
      }
    }
    int ans=0;
    while(!q.empty()){
      pair<int,int> p=q.front();
      q.pop();
      int x=p.first, y=p.second;
      if(used[x][y]) continue;
      used[x][y]=1;
      ans++;
      if(x>0){
        if(!used[x-1][y]&&a[x-1][y]=='.'){
          q.push(make_pair(x-1,y));
        }
      }
      if(x<h-1){
        if(!used[x+1][y]&&a[x+1][y]=='.'){
          q.push(make_pair(x+1,y));
        }
      }
      if(y>0){
        if(!used[x][y-1]&&a[x][y-1]=='.'){
          q.push(make_pair(x,y-1));
        }
      }
      if(y<w-1){
        if(!used[x][y+1]&&a[x][y+1]=='.'){
          q.push(make_pair(x,y+1));
        }
      }
    }
    cout<<ans<<endl;
  }
  return 0;
}

C++: #include<iostream>
#include<algorithm>

using namespace std;
int W,H;
void solve(int,int);
char dfs[20][20];
int d_x[]={1,0,-1,0},d_y[]={0,1,0,-1};
int main(){
	
	while(1){
		int ans=0;
		cin>>W>>H;
		if(W==0&&H==0)	break;

		int dx,dy;
		for(int i=0;i<H;i++){
			for(int j=0;j<W;j++){
				cin>>dfs[j][i];
				if(dfs[j][i]=='@'){
					dx=j;
					dy=i;
				}
			}
		}
		solve(dx,dy);
		for(int i=0;i<H;i++)
			for(int j=0;j<W;j++)
				if(dfs[j][i]=='T')
					ans++;
		cout<<ans<<endl;
		memset(dfs,0,sizeof(dfs));
	}
}

void solve(int x,int y){
	dfs[x][y]='T';
	
	for(int j=0;j<4;j++){
		int mx=x+d_x[j],my=y+d_y[j];
		if(mx<0||my<0||mx>W||my>H)	continue;
		if(dfs[mx][my]=='.')
			solve(mx,my);
	}
}

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

#define fi first
#define se second
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define each(itr,v) for(auto itr:v)
#define pb(s) push_back(s)
#define mp(a,b) make_pair(a,b)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define maxch(x,y) x=max(x,y)
#define minch(x,y) x=min(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt(x) bitset<32>(x).count()

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef pair<P, int> PPI;
typedef pair<ll, ll> PL;
typedef pair<P, ll> PPL;

#define INF INT_MAX/3

#define MAX_N 1000

int w,h;
string s[22];
bool vis[22][22];

int d[]={-1,0,1,0,-1};

int dfs(int y,int x){
	int res=1;
	vis[y][x]=true;
	rep(i,4){
		int nx=x+d[i],ny=y+d[i+1];
		if(nx<0||nx>=w||ny<0||ny>=h||s[ny][nx]=='#')continue;
		if(!vis[ny][nx])res+=dfs(ny,nx);
	}
	return res;
}

int main(){
	cin.sync_with_stdio(false);
	while(1){
		cin>>w>>h;
		if(w==0)break;
		int sw,sh;
		rep(i,h){
			cin>>s[i];
			rep(j,w){
				if(s[i][j]=='@'){
					sw=j; sh=i;
				}
			}
		}
		memset(vis,0,sizeof(vis));
		cout<<dfs(sh,sw)<<endl;
	}
	return 0;
}

C++: #include <cstdio>
using namespace std;
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
int a,b,sum=0;
int y[21][21]={};
char x[21][21];
void dfs(int aa,int bb){
for(int i=0;i<4;i++){
  if(aa+dx[i]>=0 && aa+dx[i]<a && bb+dy[i]>=0 && bb+dy[i]<b && y[bb+dy[i]][aa+dx[i]]==0){
y[bb+dy[i]][aa+dx[i]]=1;
dfs(aa+dx[i],bb+dy[i]);
}
}
}
int main(){
int c,d;
while(1){
scanf("%d %d",&a,&b);
if(a==0 && b==0) break;
for(int i=0;i<b;i++){
scanf("%s",x[i]);
}
for(int i=0;i<b;i++){
for(int j=0;j<a;j++){
if(x[i][j]=='.'){
y[i][j]=0;
}else if(x[i][j]=='#'){
y[i][j]=2;
}else{
	y[i][j]=1;
c=j;
d=i;
}
}}
dfs(c,d);
for(int i=0;i<b;i++){
  for(int j=0;j<a;j++){
    if(y[i][j]==1){
      sum++;
    }
  }
}
printf("%d\n",sum);
sum=0;
}
return 0;
}

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

int h, w, ans;
char field[25][25];

int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, -1, 0, 1};

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

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

    ans = 0;
    dfs(sx, sy);
    cout << ans << endl;
  }
}