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++: #if 0
08-162015?????????????????°???????????????????????????
pair???
#endif

#include <iostream>
#include <queue>
#include <string.h>
#include <utility>
using namespace std;

int w,h;
int tot=1; //?????£????????????(?????????????????????)
const int dx[]={1,0,-1,0}, dy[]={0,-1,0,1}; //??????????§??????¨
char P[30][30]; //??§?¨?????????????????????¨???

bool valid(int x,int y){ //??????????????????
	return (x>=0)&&(x<w)&&(y>=0)&&(y<h)&&(P[x][y]!='#');
}

void bfs(int x,int y){ //???????????¢?´¢
	queue<pair<int,int> > q;
	pair<int,int> p;
	p = make_pair(x,y); //pair??????????????¨??????????????????
	q.push(p);
	while(!q.empty()){
		pair<int,int> cur=q.front(); //?????¨??°?????????????????????
		q.pop();
		for(int i=0;i<4;++i){
			if(valid(cur.first+dx[i],cur.second+dy[i]))
				tot+=1;
				P[cur.first+dx[i]][cur.second+dy[i]]='#'; //???????????£?????´???????°???????
				q.push(make_pair(cur.first+dx[i],cur.second+dy[i]));
				cur.first+=dx[i]; cur.second+=dy[i];
				q.push(cur);
		}
	}
}

int main(){
	int x1,y1;
	while((cin>>w>>h)&&(w!=0&&h!=0)){
		for(int i=0;i<h;++i){
			for(int j=0;j<w;++j){
				cin>>P[i][j];
				if(P[i][j]=='@')
					x1=i; y1=j; 
			}
		}
		bfs(x1,y1); //??????????????°????????£??\????????¢?´¢????§?
		cout << tot << endl;
	}
}

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

int w, h;
char tile[20][20];
int cnt = 0;
int dx[4] = { 1, -1, 0, 0 };
int dy[4] = { 0, 0, 1, -1 };

void f(int x, int y){
	tile[x][y] = '#';
	cnt++;
	for (int i = 0; i < 4; i++){
		int X = x + dx[i];
		int Y = y + dy[i];
		if (tile[X][Y] == '.' && 0 <= x && x < w && 0 <= y && y < h){
			f(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[x][y];
			}
		}

		for (int y = 0; y < h; y++){
			for (int x = 0; x < w; x++){
				if (tile[x][y] == '@') f(x, y);
			}
		}

		cout << cnt << endl;
		cnt = 0;
	}

	return 0;
}

C++: #include <bits/stdc++.h>
#define REP(i,n) for (long long i=0;i<(n);i++)
#define FOR(i,a,b) for (long long i=(a);i<(b);i++)
#define RREP(i,n) for(long long i=n;i>=0;i--)
#define RFOR(i,a,b) for(long long i=(a);i>(b);i--)
#define dump1d_arr(array) REP(i,array.size()) cerr << #array << "[" << (i) << "] ==> " << (array[i]) << endl
#define dump2d_arr(array) REP(i,array.size()) REP(j,array[i].size()) cerr << #array << "[" << (i) << "]" << "[" << (j) << "] ==> " << (array[i][j]) << endl
#define dump(x)  cerr << #x << " => " << (x) << endl
#define dumpP(p) cerr << "( " << p.first << " , " << p.second << " )" << ends
#define SORT(c) sort((c).begin(),(c).end())
#define MIN(vec) *min_element(vec.begin(), vec.end())
#define MAX(vec) *max_element(vec.begin(), vec.end())
#define UNIQ(vec) vec.erase(unique(vec.begin(), vec.end()),vec.end()) //ソートの必要あり
#define IN(n,m)  (!(m.find(n) == m.end()))
#define ENUM(m) for (auto itr = m.begin(); itr != m.end(); ++itr)
#define dump_MAP(m) for(auto itr = m.begin(); itr != m.end(); ++itr) { cerr << itr->first << " --> "  << itr->second << endl; }
#define FINDL(vec,x) (lower_bound(vec.begin(),vec.end(),x) - vec.begin())
#define FINDU(vec,x) (upper_bound(vec.begin(),vec.end(),x) - vec.begin())
#define ROUND(N) setprecision(N)
#define ROUND_PRINT(N,val) cout << fixed;cout << setprecision(N) << val << endl
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define INARR(h,w,x,y) (0 <= y && y < h && 0 <= x && x < w)

using namespace std;
constexpr int dx[4] = {0,1,0,-1};
constexpr int dy[4] = {1,0,-1,0};
constexpr long double pi = M_PI;
constexpr double eps = 1e-10;
constexpr long mod = 1000000007;
constexpr short shINF = 32767;
constexpr long loINF = 2147483647;
constexpr long long llINF = 9223372036854775807;
typedef long long LL;
typedef vector<bool> VB;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<LL,LL> pr;
typedef vector<pr> VP;
struct Order {
	bool operator() (pr const& a,pr const& b) const {
		return a.first > b.first || ((a.first == b.first) && (a.second > b.second));
	}
};

VVI arr;
vector<VB> used;
long H,W;
void dfs(int x,int y) {
	if (!INARR(H,W,x,y)) return;
	if (used[y][x] || !arr[y][x]) return;
	else {
		used[y][x] = true;
		REP(i,4) dfs(x+dx[i],y+dy[i]);
	}
}
int main(void) {
	while (1) {
	cin >> W >> H;
	if (W == 0 && H == 0) break;
	arr = VVI(H,VI(W));
	used = vector<VB>(H,VB(W,false));
	char s;
	int x,y;
	REP(i,H) {
		REP(j,W) {
			cin >> s;
			if (s == '#') arr[i][j] = 0;
			else arr[i][j] = 1;
			if (s == '@') {
				x = j;y = i;
			}
		}
	}
	dfs(x,y);
	long cnt = 0;
	REP(i,H) REP(j,W) if (used[i][j]) cnt++;
	cout << (cnt) << endl;

	}
}