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>
using namespace std;
int w, h, cnt;
int vx[] = {0, 1, 0, -1};
int vy[] = {1, 0, -1, 0};
char field[20][20];
void solve(int x, int y){
    ++cnt;
    field[y][x] = '#';
    for(int i = 0; i < 4; ++i){
        int nx = x + vx[i];
        int ny = y + vy[i];
        if(nx >= 0 && nx < w && ny >= 0 && ny < h && field[ny][nx] == '.')
            solve(nx, ny);
    }
}
int main(){
    int sx, sy;
    while(cin >> w >> h){

        if(!(w || h)) break;
        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;
                }
            }
        }
        cnt = 0;

        solve(sx, sy);
        cout << cnt << endl;
    }
}

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

using namespace std;

int w, h;
string str[30];

int search(int y, int x){
	if(x < 0 || x >= w || y < 0 || y >= h){
		return 0;
	}
	if(str[y][x] == '#'){
		return 0;
	}
	str[y][x] = '#';
	int ret = 1;
	ret += search(y, x - 1);
	ret += search(y, x + 1);
	ret += search(y - 1, x);
	ret += search(y + 1, x);
	return ret;
}

int main(){
	
	while(true){
		cin >> w >> h;
		if(w == 0 && h == 0){
			break;
		}
		for(int i = 0; i < h; i++){
			cin >> str[i];
		}
		int ans;
		for(int i = 0; i < h; i++){
			for(int j = 0; j < w; j++){
				if(str[i][j] == '@'){
					ans = search(i, j);
				}
			}
		}
		cout << ans << endl;
	}
	
	return 0;
}

C++: #include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <climits>

#define rep(i, m, n) for(int i=int(m);i<int(n);i++)
#define EACH(i, c) for (auto &(i): c)
#define all(c) begin(c),end(c)
#define EXIST(s, e) ((s).find(e)!=(s).end())
#define SORT(c) sort(begin(c),end(c))
#define pb emplace_back
#define MP make_pair
#define SZ(a) int((a).size())

//#define LOCAL 0
//#ifdef LOCAL
//#define DEBUG(s) cout << (s) << endl
//#define dump(x)  cerr << #x << " = " << (x) << endl
//#define BR cout << endl;
//#else
//#define DEBUG(s) do{}while(0)
//#define dump(x) do{}while(0)
//#define BR
//#endif


//改造
typedef long long int ll;
using namespace std;
#define INF (1 << 30)
#define INFl (ll)5e15
#define DEBUG 0 //デバッグする時1にしてね
#define dump(x)  cerr << #x << " = " << (x) << endl
#define MOD 1000000007
//ここから編集する
int w,h;
bool valid(int y,int x){
    return y >= 0 && x >= 0 && y < h && x < w;
}
int dfs(int y,int x,vector<vector<int> > &v){
    if(v[y][x] != 0){
        return 0;
    }
    v[y][x] = 3;
    int ret = 1;
    if(valid(y+1,x)){
        ret += dfs(y+1,x,v);
    }
    if(valid(y-1,x)){
        ret += dfs(y-1,x,v);
    }
    if(valid(y,x+1)){
        ret += dfs(y,x+1,v);
    }
    if(valid(y,x-1)){
        ret += dfs(y,x-1,v);
    }
    return ret;
}
void solve(int W,int H){
    vector<vector<int> > v(H,vector<int>(W));
    w = W;
    h = H;
    int sy,sx;
    rep(i,0,H){
        rep(j,0,W){
            char tmp;
            cin >> tmp;
            if(tmp == '@'){
                sy = i;
                sx = j;
                v[i][j] = 0;
            }else if(tmp == '.'){
                v[i][j] = 0;
            }else if(tmp == '#'){
                v[i][j] = 1;
            }
        }
    }
    cout << dfs(sy,sx,v) << endl;

}

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

    while(true){
        int W,H;
        cin >> W >> H;
        if(W == 0) break;
        solve(W,H);


    }


    return 0;
}

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[j][i];
				if(P[j][i]=='@')
					x1=j; y1=i; 
			}
		}
		bfs(x1,y1); //??????????????°????????£??\????????¢?´¢????§?
		cout << tot << endl;
	}
}