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<string>
#include<algorithm>
#include<vector>
#include<iomanip>
#include<math.h>
#include<complex>
#include<queue>
#include<deque>
#include<stack>
#include<map>
#include<set>
#include<bitset>
#include<functional>
#include<assert.h>
#include<numeric>
using namespace std;
#define REP(i,m,n) for(int i=(int)(m) ; i < (int) (n) ; ++i )
#define rep(i,n) REP(i,0,n)
using ll = long long;
const int inf=1e9+7;
const ll longinf=1LL<<60 ;
const ll mod=1e9+7 ;
int d[]={1,0,-1,0,1};

void solve(int w,int h){
    string s[h];
    rep(i,h)cin>>s[i];
    int sx,sy;
    rep(i,h)rep(j,w)if(s[i][j]=='@')sx=i,sy=j;
    queue<pair<int,int>> que;
    que.emplace(sx,sy);
    vector<vector<int>> used(h,vector<int>(w));
    used[sx][sy]=1;
    int ans=1;
    while(que.size()){
        int x=que.front().first,y=que.front().second;
        que.pop();
        rep(i,4){
            int nx=x+d[i],ny=y+d[i+1];
            if(nx<0||nx>=h||ny<0||ny>=w)continue;
            if(used[nx][ny]||s[nx][ny]=='#')continue;
            ++ans;
            used[nx][ny]=1;
            que.emplace(nx,ny);
        }
    }
    cout<<ans<<endl;
}


int main(){
    int n,m;
    while(cin>>n>>m,n!=0)solve(n,m);
    return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
bool c[22][22] = {} ;
int cnt,w, h, p[22][22] = {};

int main() {
	int j, f,cx,cy;
	char in[20];
	while (1) {
		for (int i = 0; i < 484; i++) {
			c[i / 22][i % 22] = p[i / 22][i % 22] = 0;
		}
		cnt = 0;
		f = 1;
		scanf("%d %d", &w, &h);
		if (w ==0&& h == 0)
			break;
		scanf("\n", &j);
		for (int i = 0; i < h; i++) {
			scanf("%s", &in);
			for (j = 0; j < w; j++) {
				switch (in[j]) {
				case '#':
					c[j+1][i+1] = 0;
					p[j+1][i+1] = -1;
					break;
				case '@':
					cx = j;
					cy = i;
					p[j+1][i+1] = 1;
				case '.':
					c[j+1][i+1] = 1;
				}
			}
		}

		/*for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++)
				printf("%3d", c[j][i]);
			printf("\n");
		}*/

		while (f == 1) {
			f = 0;
			for (int i = 0; i < h; i++) {
				for (int j = 0; j < w; j++)
					printf("%3d", p[j+1][i+1]);
				printf("\n");
			}
			printf("\n");
			if (w != 1 && h != 1) {
				for (int i = 0; i < w*h; i++) {
					if (p[i / h+1][i%h+1] == 0 && (p[i / h + 2][i % h+1] == 1 || p[i / h][i % h+1] == 1 || p[i / h+1][i % h + 2] == 1 || p[i / h+1][i % h] == 1)) {
						p[i / h+1][i%h+1] = 1;
						f = 1;
					}
				}
			}
			if (w == 1 && h != 1) {
				for (int i = 0; i < h; i++) {
					if (p[1][i+1] == 0 && (p[1][i + 2] == 1 || p[0][i] == 1)) {
						p[1][i+1] = 1;
						f = 1;
					}
				}
			}

			if (w != 1 && h == 1) {
				for (int i = 0; i < w; i++) {
					if (p[i+1][1] == 0 && (p[i + 2][1] == 1 || p[i][1] == 1)) {
						p[i+1][1] = 1;
						f = 1;
					}
				}
			}
		}

		for (int i = 0; i < w*h; i++) {
			if (p[i / h+1][i%h+1] == 1)
				cnt++;
		}
		printf("%d\n", cnt);
	}
	return 0;
}

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

#define ll long long
#define vvi vector<vector<int>>
#define vec vector
#define pq priority_queue
#define all(v) (v).begin(), (v).end()
#define rep(i, n) for (int (i) = (0); (i) < (n); ++(i))
#define repp(i, m, n) for (int (i) = (m); (i) < (n); ++(i))
#define debug(x) cerr << #x << ": " << x << endl;
#define debug2(x, y) cerr<<"("<<#x<<", "<<#y<<") = "<<"("<<x<<", "<<y<<")"<<endl;
#define debug3(x, y, z) cerr<<"("<<#x<<", "<<#y<<", "<<#z<<") = "<<"("<<x<<", "<<y<<", "<<z<<")"<<endl;
#define debugB(x, y) cerr<<#x<<": "<<bitset<y>(x) << endl;
#define line() cerr << "---------------" << endl;

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

template<typename T>
void printA(vector<T> &printArray, char between = ' ') {
   int paSize = printArray.size();
   for (int i = 0; i < paSize; i++) { cerr << printArray[i] << between;}
   if (between != '\n') {cerr << endl;}
}

// ------------------------------------------------------------------------------------------

int W, H;
char B[30][30];
int cnt = 0;

void dfs(int y, int x) {
   cnt++;
   B[y][x] = '#';
   rep (i, 4) {
      int nx = x+dx[i], ny = y+dy[i];
      if (nx < 0 || nx >= W || ny < 0 || ny >= H || B[ny][nx] == '#') continue;
      dfs(ny, nx);
   }
}

int main() {
   while (1) {
      cin >> W >> H;
      if (W == 0 && H == 0) break;
      cnt = 0;
      rep (i, H) {
         cin >> B[i];
      }
      rep (i, H) {
         rep (j, W) {
            if (B[i][j] == '@') {
               dfs(i, j);
            }
         }
      }
      cout << cnt << endl;
   }

   return 0;
}