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<stdio.h>

int m,n,ans;
char ice[22][22];

void saiki(int w,int h){
	ice[w+1][h]='*';
	
	if(ice[w+2][h]=='.')saiki(w+1,h);
	if(ice[w+1][h+1]=='.')saiki(w,h+1);
	if(ice[w][h]=='.')saiki(w-1,h);
	if(h!=0)if(ice[w+1][h-1]=='.')saiki(w,h-1);
}

int main(void){

	for(;;){
		scanf("%d %d",&m,&n);
		if(!m||!n)break;
		
		ans=0;
		
		for(int i=0;i<n;i++){
			scanf("%s",&ice[i+1]);
		}
		
		for(int i=0;i<n;i++){
			for(int j=0;j<m;j++){
				if(ice[i+1][j]=='@')saiki(i,j);
			}
		}
		for(int i=0;i<n;i++){
			for(int j=0;j<m;j++){
				if(ice[i+1][j]=='*')ans++;
			}
		}
		printf("%d\n",ans);
	}
	return 0;
}

C++: #include<iostream>
using namespace std;
char tile[21][21];

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

int sum=0;

void check(int x,int y)
{
  if(tile[x][y]=='#')
    return;
  sum++;
  tile[x][y]='#';
  for(int i=0;i<4;i++)
    {
      if(x+dx[i]>=0 &&x+dx[i]<21 &&y+dy[i]>=0 &&y+dy[i]<21)
	{
	  check(x+dx[i],y+dy[i]);
	}
    }
}

int main()
{
  int w,h;
  for(;cin>>w>>h,w||h;)
    {
      for(int i=0;i<21;i++)
	  for(int j=0;j<21;j++)
	      tile[i][j]='#';
      
      int x,y;
      for(int i=0;i<h;i++)
	for(int j=0;j<w;j++)
	  {
	    cin>>tile[j][i];
	    if(tile[j][i]=='@')
	      {
		x=j,y=i;
	      }
	  }
      sum=0;
      check(x,y);
      cout<<sum<<endl;
      /*
      for(int i=0;i<h;i++,cout<<endl)
	for(int j=0;j<w;j++)
	  {
	    cout<<tile[j][i];
	  }
      */
    }
}

C++: #include <bits/stdc++.h>
#define INF 1e18
#define int long long
#define Rep(i, a, n) for (int i = (a); i < (n); i++)
#define rep(i, n) Rep(i, 0, n)
#define all(a) (a).begin(), (a).end()
using namespace std;
typedef pair<int, int> P;
typedef pair<int, P> PP;
const int mod = 1000000007;
//const int mod = 998244353;

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

bool in(int y, int x) { return 0 <= y && y < h && 0 <= x && x < w; }

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    while (1)
    {
        cin >> w >> h;
        if (w == 0 && h == 0)
            break;
        vector<string> s(h);
        rep(i, h) cin >> s[i];
        queue<P> que;
        int vis[30][30] = {};
        rep(i, h) rep(j, w) if (s[i][j] == '@')
        {
            que.push({i, j});
            vis[i][j] = 1;
        }
        int ans = 1;
        while (!que.empty())
        {
            P p = que.front();
            que.pop();
            int y = p.first, x = p.second;
            rep(i, 4)
            {
                int ny = y + dy[i], nx = x + dx[i];
                if (!in(ny, nx) || vis[ny][nx] || s[ny][nx] == '#')
                    continue;
                vis[ny][nx] = 1;
                ans++;
                que.push({ny, nx});
            }
        }
        cout << ans << endl;
    }
}

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

using namespace std;

int dxdy[4][2] = { {-1,0}, {1,0}, {0,1}, {0,-1} };

int fill(vector<vector<char> >& v, int mi, int mj){
    int sum = 0;
    for(int i=0; i < 4; ++i){
        if(v[ mi+dxdy[i][0] ][ mj+dxdy[i][1] ] == '.'){
            sum++;
            v[mi+dxdy[i][0]][mj+dxdy[i][1]] = ':';
            sum += fill(v, mi + dxdy[i][0], mj + dxdy[i][1]);
        }
    }
    return sum;
}

int main(){
    int w, h;
    int mi, mj;
    char c;
    while(true){
        cin >> w;
        cin >> h;
        if(w == 0 && h == 0) break;
        vector<vector<char> > v(w+2, vector<char>(h+2));
        for(int j = 0; j <= h+1; ++j){
            for(int i = 0; i <= w+1; ++i){
                if(i == 0 || j == 0 || i == w+1 || j == h+1 ){
                    v[i][j] = '#';
                } else {
                    cin >> c;
                    if(c == '@') {
                        mi = i, mj = j;
                        c = ':';
                    }
                    v[i][j] = c;
                }
            }
            if( j >= 1 && j <= h ) cin.ignore();
        }

        cout << fill(v, mi, mj) + 1 << endl;
    }
}

C++: #include<cstdio>
#include<cstring>
#include<vector>
#include<queue>
#include<algorithm>
#include<cmath>
#include<climits>
#include<string>
#include<set>
#include<numeric>
#include<map>
#include<iostream>
using namespace std;
#define rep(i,n) for(int i = 0;i<((int)(n));i++)
#define reg(i,a,b) for(int i = ((int)(a));i<=((int)(b));i++)
#define irep(i,n) for(int i = ((int)(n)-1);i>=0;i--)
#define ireg(i,a,b) for(int i = ((int)(b));i>=((int)(a));i--)
typedef long long ll;
typedef pair<ll, ll> mp;

int W,H,f[20][20],ans[50],cnt=0,sx,sy;
string m[20],t,s;

void find(int x,int y){
	if(x>=W || x<0 || y>=H || y<0)return;
	t = m[x][y];
	if(t=="#")return;
	if(f[x][y]!=0)return;
	f[x][y] = 1;
	ans[cnt]++;
	find(x+1,y);
	find(x-1,y);
	find(x,y+1);
	find(x,y-1);
}

int main(void){
	while(1){
		cin>>W>>H;
		if(W==0 && H==0)break;
		ans[cnt]=0;
		rep(i,H){
			cin>>s;
			rep(j,W){
				f[j][i]=0;
				m[j][i]=s[j];
				t=m[j][i];
				if(t=="@"){
					sx=j;
					sy=i;
				}
			}
		}
		find(sx,sy);
		cnt++;
	}
	rep(i,cnt)cout<<ans[i]<<endl;
	return 0;
}

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

using namespace std;

int h,w;
char grid[21][21];
int dx[4]={0,1,0,-1};
int dy[4]={1,0,-1,0};

int dfs(int x,int y){
  if(grid[y][x]=='#')return 0;
  grid[y][x]='#';
  int sum=1;
  for(int i=0;i<4;i++){
    int nx=x+dx[i],ny=y+dy[i];
    if(0<=nx && nx<w && 0<=ny && ny<h)sum+=dfs(nx,ny);
  }
  return sum;
}

int main(void){

  while(cin >> w >> h,w|h){
    for(int i=0;i<h;i++)cin >> grid[i];
    
    for(int y=0;y<h;y++)
      for(int x=0;x<w;x++)
	if(grid[y][x]=='@')cout << dfs(x,y) << endl;
  }

  return 0;
}