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};

string field[];

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

C++: //
//AOJ volume11 1130
//http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=1130&lang=jp
//20170605
//640009E
//Yang Bo
//

#include <iostream>
#include <vector>

using namespace std;

int w, h;
int starty, startx;
vector< vector<char> > a(20, vector<char>(20, 'a')); //??£??\??????

int recursion(char iny, char inx)
{
  a[iny][inx] = '#';
  int number = 0;
  if (inx < w - 1)
    if (a[iny][inx + 1] == '.')
      number += recursion(iny, inx + 1);
  if (iny < h - 1)
    if (a[iny + 1][inx] == '.')
      number += recursion(iny + 1, inx);
  if (inx > 0)
    if (a[iny][inx - 1] == '.')
      number += recursion(iny, inx - 1);
  if (iny > 0)
    if (a[iny - 1][inx] == '.')
      number += recursion(iny - 1, inx);
  number += 1;
  return number;
  //cout << " recursion(" << iny << ", "<< inx << ") = " << number << endl; 
}

int main()
{
  while (cin >> w >> h) {
    if (w == 0)
      break;
    else {
      for (int i = 0; i < h; i++) {
	for (int j = 0; j < w; j++) {
	  cin >> a[i][j]; //??\???
	  if (a[i][j] == '@') {
	    starty = i;
	    startx = j;
	    //cout << "i = " << i << ", j = " << j << endl;
	  }
	}
      }
      int ans = recursion(starty, startx);
      cout << ans << endl;
    }
  }
}

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

#define rep(i,n) rep2(i,0,n)
#define rep2(i,m,n) for(int i=m;i<n;i++)

int w,h,ans,dy[]={-1,0,1,0},dx[]={0,-1,0,1};
char c[22][22];

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

int main(){
	while(cin>>w>>h&&w){
		ans=0;
		int y,x;
		rep(i,h)rep(j,w){
			cin>>c[i][j];
			if(c[i][j]=='@')y=i,x=j;
		}
		dfs(y,x);
		cout<<ans<<endl;
	}
}

C++: #include <iostream>
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <bitset>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
using namespace std;
typedef long long ll;
typedef pair<int,int> pint;
typedef vector<int> vint;
typedef vector<pint> vpint;
#define mp make_pair
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define REP(i,n) for (int i=(n)-1;i>=0;i--)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define REPS(i,f,n) for (int i=(f)-1;i>=(n);i--)
int dx[4] = {1, 0, 0, -1};
int dy[4] = {0, 1, -1, 0};

char board[21][21];
int w, h;
int x, y;// ?????¨?????????

void slove(void){
	int cnt = 0;
	queue<pint> q;
	q.push(make_pair(y, x));//?????¨????????????queue?????\??????

	while(!q.empty()){
		pint now = q.front(); q.pop();
		rep(i, 4){
			int nowy = now.fi + dy[i];
			int nowx = now.se + dx[i];
			if (0 <= nowy <= h - 1 && 0 <= nowx && nowx <= w - 1){
				if (board[nowy][nowx] == '.'){
					cnt++;
					board[nowy][nowx] = 0;
					q.push(make_pair(nowy, nowx));
				}
			}
		}
	}
	printf("%d\n", cnt + 1);//?§?????????´????????\??????
	return;
}

void scan(int w, int h){
	rep(i, h){
		rep(j, w){
			cin >> board[i][j];
			if (board[i][j] == '@'){
				y = i; x = j;
			}
		}
		getchar();
	}
	/*
	rep(i, h){
		rep(j, w){
			printf("%c", board[i][j]);
		}
		printf("\n");
	}
	*/
	slove();
	return;
}

int main(void){
	rep(i, 1000){
		cin >> w >> h;

		if (w == 0) break;
		scan(w, h);
	}
	return 0;
}

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

void solve(int x,int y,int MAP[20][20],int s,int n);

int main()
{
    int x,y,num,size;
    char c;
    int MAP[20][20];

    while(cin >> size >> num , size && num)
    {
        int cnt = 0;

        for(int i=0; i<num; i++){
            for(int j=0; j<size; j++){
                cin >> c;
                if(c == '.'){
                    MAP[i][j] = 0;
                }
                if(c == '#'){
                    MAP[i][j] = 1;
                }
                if(c == '@'){
                    x = j;
                    y = i;
                    MAP[i][j] = 0;
                }
            }
        }

        solve(x,y,MAP,size,num);
        for(int i=0; i<num; i++){
            for(int j=0; j<size; j++){
                if(MAP[i][j] == 2)cnt++;
            }
        }

        cout << cnt << endl;
    }

    return 0;
}

void solve(int x,int y,int MAP[20][20],int s,int n)
{
    MAP[y][x] = 2;

    if(x-1 >= 0){
        if(MAP[y][x-1] == 0){
            solve(x-1,y,MAP,s,n);
        }
    }
    if(x+1 < s){
        if(MAP[y][x+1] == 0){
            solve(x+1,y,MAP,s,n);
        }
    }
    if(y-1 >= 0){
        if(MAP[y-1][x] == 0){
            solve(x,y-1,MAP,s,n);
        }
    }
    if(y+1 < n){
        if(MAP[y+1][x] == 0){
            solve(x,y+1,MAP,s,n);
        }
    }

    return;
}