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 <cstdio>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <queue>
using namespace std;

struct state { int y, x, step; };
static const int dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};

int main() {
        int w, h;
        while (scanf("%d%d", &w, &h), w) {
                vector<string> s(h);
                for (int i = 0; i < h; i ++) cin >> s[i];
                int sy, sx;
                for (int i = 0; i < h; i ++) {
                        for (int j = 0; j < w; j ++) {
                                if (s[i][j] == '@') {
                                        sy = i, sx = j;
                                }
                        }
                }
                vector<vector<bool>> used(h, vector<bool>(w, false));
                queue<state> q;
                q.push({sy, sx, 0});
                used[sy][sx] = true;
                while (!q.empty()) {
                        state p = q.front(); q.pop();
                        for (int d = 0; d < 4; d ++) {
                                int xx = p.x + dx[d], yy = p.y + dy[d];
                                if (xx < 0 || xx >= w || yy < 0 || yy >= h) continue;
                                if (used[yy][xx] || s[yy][xx] == '#') continue;
                                used[yy][xx] = true;
                                q.push({yy, xx, p.step + 1});
                        }
                }
                int ans = 0;
                for (int i = 0; i < h; i ++) {
                        for (int j = 0; j < w; j ++) {
                                ans += used[i][j];
                        }
                }
                printf("%d\n", ans);
        }
        return 0;
}

C++: #include<stdio.h>
#include<stdlib.h>
#include<iostream>
#include<string.h>
#include<math.h>
#include<cstring>
using namespace std;

int main(){
	while(1){
		int i,j,k,w,h,a;
		char c[20][20];
		cin>>w>>h;
		if(w==0&&h==0)break;
		for(i=0;i<20;i++){
			for(j=0;j<20;j++){
				c[i][j]='\0';
			}
		}
		
		
		for(i=0;i<h;i++){
			cin>>c[i];
		}
		for(k=0;k<=w*h;k++){
			for(i=0;i<h;i++){
				for(j=0;j<w;j++){
					if(c[i][j]=='.'){
						if(c[i][j+1]=='@'||c[i][j-1]=='@'||c[i-1][j]=='@'||c[i+1][j]=='@'){
							c[i][j]='@';
						}
					}	
				}
			}
		}
		

		a=0;
		for(i=0;i<h;i++){
			for(j=0;j<w;j++){
				if(c[i][j]=='@')a++;	
			}
		}
		cout<<a<<endl;
	}
    return 0;
}

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

char map[20][20];

int W, H, start_x, start_y, ans = 0;

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

void dfs(int x, int y)
{
  ans++;
  if(map[x][y] != '#'){
    map[x][y] = '#';
    for(int i = 0; i < 4; i++){
      int next_x = x + dx[i], next_y = y + dy[i];
      if(next_x < W && next_x >= 0 && next_y < H && next_y >= 0){
	if(map[next_x][next_y] == '#')
	  continue;
	dfs(next_x, next_y);
      }else{
	continue;
      }
    }
  }
}

int main()
{
  while(1){
    cin >> W >> H;
    if(W == 0 && H == 0){
      break;
    }else{
      for(int i = 0; i < H; i++){
	for(int j = 0; j < W; j++){
	  cin >> map[j][i];
	  if(map[j][i] == '@'){
	    start_x = j;
	    start_y = i;
	  }
	}
      }
      dfs(start_x, start_y);
      cout << ans << endl;
      ans = 0;
    }
  }
}

C++: #include<iostream>
#include<string>
#include<queue>
#include<vector>
using namespace std;
#define frp(i,n) for((i)=0;(i)<(n);i++)
int vx[4]={0,1,0,-1};
int vy[4]={1,0,-1,0};
int H,W;
int check(int n1,int n2,int rednum,vector<int> red1,vector<int> red2){
  for(int i=0;i<rednum;i++){
    if(n1==red1[i]&&n2==red2[i]||n1<0||n2<0||n1>=H||n2>=W){
      return 0;
    }
  }
  return 1;
}
int main(){
  int i,j,now1,now2;
  while(cin>>W>>H,W+H!=0){
    int num=1;
    string str2;
    vector<string> str;
    vector<int> red1;
    vector<int> red2;
    frp(i,H){
      cin>>str2;
      str.push_back(str2);
    }
    frp(i,H){
      frp(j,W){
	if(str[i][j]=='#'){
	  red1.push_back(i);
	  red2.push_back(j);
	}
      }
    }
    queue<pair<int,int> > qii;
    frp(i,H){
      frp(j,W){
	if(str[i][j]=='@'){
	  qii.push(make_pair(i,j));
	  red1.push_back(i);
	  red2.push_back(j);
	}
      }
    }
    while(!qii.empty()){
      now1=qii.front().first;
      now2=qii.front().second;
      qii.pop();
      for(i=0;i<4;i++){
	if(check(now1+vx[i],now2+vy[i],red1.size(),red1,red2)==1){
	  red1.push_back(now1+vx[i]);
	  red2.push_back(now2+vy[i]);
	  qii.push(make_pair(now1+vx[i],now2+vy[i]));
	  num++;
	}
      }
    }
    cout<<num<<endl;
  }
  return 0;
}

C++: #include<iostream>
using namespace std;
void counts(int h,int w);
int check[31][31]={0};
char s[31][31];
int dh[4]={-1,0,1,0};
int dw[4]={0,1,0,-1};
int ww,hh;
int counta=0;
main(){
  int sw,sh,countx;
  while(1){
    cin>>ww>>hh;
    if(ww==0&&hh==0) break;
    for(int i=1;i<=hh;i++){
      for(int j=1;j<=ww;j++){
	cin>>s[i][j];
	if(s[i][j]=='@'){
	  sh=i;
	  sw=j;
	}
      }
    }
    counts(sh,sw);
    cout<<counta<<endl;
    for(int i=0;i<=30;i++){
      for(int j=0;j<=30;j++){
	check[i][j]=0;
      }
    }
    counta=0;
  }
}
void counts(int h,int w){
  check[h][w]=1;
  counta++;
  for(int i=0;i<8;i++){
    int nh=h+dh[i];
    int nw=w+dw[i];
    if(nh>=1&&nh<=hh&&nw>=1&&nw<=ww&&s[nh][nw]=='.'&&check[nh][nw]==0){
      counts(nh,nw);
    }
  }
  return;
}