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[100][100]; //??§?¨?????????????????????¨???

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;
				q.push(make_pair(cur.first+dx[i],cur.second+dy[i]));
				P[cur.first+dx[i]][cur.second+dy[i]]='#'; //???????????£?????´???????°???????
			}
		}
		P[cur.first][cur.second]='#';
	}
}

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<stdio.h>
char a[21][21];
int c;
void dfs(int y,int x){
  c++;
  a[y][x]=0;
  if(a[y-1][x]=='.')dfs(y-1,x);
  if(a[y+1][x]=='.')dfs(y+1,x);
  if(a[y][x-1]=='.')dfs(y,x-1);
  if(a[y][x+1]=='.')dfs(y,x+1);
  return;
}
int main(){
  int w,h,i,j;
  while(1){
    scanf("%d%d",&w,&h);
    if(w==0&&h==0)break;
    for(i=0;i<21;i++){
      for(j=0;j<21;j++){
	a[i][j]=0;
      }
    }
    for(i=0;i<h;i++){
      for(j=0;j<=w;j++){
	scanf("%c",&a[i][j]);
      }
    }
    c=0;
    for(i=0;i<h;i++){
      for(j=0;j<w;j++){
	if(a[i][j]=='@')dfs(i,j);
      }
    }
    printf("%d\n",c);

   
  }
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
const int inf = 1001001001;


int w, h;
int a[20][20];
int sw, sh;
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
int D[20][20];
int Ans = 1;


int main()
{
    while(cin >> w, w != 0)
    {
        Ans = 1;
        cin >> h;
        
        for(int i = 0; i < 20; i++)
        {
            for(int j = 0; j < 20; j++)
            {
                D[i][j] = inf;
            }
        }
        
        for(int i = 0; i < h; i++)
        {
            for(int j = 0; j < w; j++)
            {
                char x;
                cin >> x;
                if(x == '.')
                {
                    a[j][i] = 1;
                }
                else if(x == '#')
                {
                    a[j][i] = 0;
                }
                else
                {
                    sw = j;
                    sh = i;
                    a[j][i] = 100;  //  ????????§?????????
                }
            }
        }
        queue< pair<int, int> > Q;
        pair<int, int> S;
        S = make_pair(sw, sh);
        Q.push(S);
        D[sw][sh] = 0;
        int k = 0;
        while(! Q.empty())
        {
            pair<int, int> cur = Q.front();
            Q.pop();
            int x = cur.first;
            int y = cur.second;
            for(int i = 0; i < 4; i++)
            {
                if(a[x+dx[i]][y+dy[i]] == 1 && 0 <= x+dx[i] && x+dx[i] < w && 0 <= y+dy[i] && y+dy[i] < h && D[x+dx[i]][y+dy[i]] == inf)    //  ????????????????¢????????????????????????????????????°???
                {
                    D[x+dx[i]][y+dy[i]] = D[x][y] + 1;
                    Ans = Ans + 1;
                    pair<int, int> T;
                    T = make_pair(x+dx[i], y+dy[i]);
                    Q.push(T);
                }
            }
        }
        cout << Ans << endl;
    }
}

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

char map[20][20];
int visited[20][20];

void dfs(int x, int y, int w, int h) {
    visited[x][y] = 1;
    for (int i = -1; i <= 1; i += 2) {
        if (0 <= x+i && x+i < h && visited[x+i][y] == 0 && map[x+i][y] == '.')
            dfs(x+i, y, w, h);
    }
    for (int i = -1; i <= 1; i += 2) {
        if (0 <= y+i && y+i < w && visited[x][y+i] == 0 && map[x][y+i] == '.')
            dfs(x, y+i, w, h);
    }
}

int main(int argc, char *argv[])
{
    int w, h, x, y, sum;
    string line;
    while (cin >> w >> h, w | h) {
        for (int i = 0; i < 20; ++i)
            for (int j = 0; j < 20; ++j)
                visited[i][j] = 0;
        for (int i = 0; i < h; ++i) {
            cin >> line;
            for (int j = 0; j < w; ++j) {
                map[i][j] = line[j];
                if (line[j] == '@') {
                    x = i;
                    y = j;
                }
            }
        }
        dfs(x, y, w, h);
        sum = 0;
        for (int i = 0; i < 20; ++i)
            for (int j = 0; j < 20; ++j)
                sum += visited[i][j];
        cout << sum << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm> 
#include <queue>
#include <functional>
#include <map>
#include <string>
using namespace std;
int w, h;
char field[25][25];
bool used[25][25];
int vx[] = { 1, 0, -1, 0 };
int vy[] = { 0, 1, 0, -1 };

int dfs(int x,int y){
    
    int ret = 1;
    used[x][y] = true;

    for (int i = 0; i < 4; i++){
        int nx, ny;
        nx = x + vx[i]; ny = y + vy[i];
        if (nx != 0 && nx != w + 1 && ny != 0 && ny != h + 1 && field[nx][ny] != '#'&&
            !used[nx][ny]){
            ret += dfs(nx, ny);
        }
    }

    return ret;
}

int main(void){

    while (true){
        cin >> w >> h;
        if (w == 0 && h == 0)break;
        for (int i = 1; i <= w; i++){
            for (int j = 1; j <= h; j++){
                used[i][j] = false;
            }
        }
        int sx, sy;
        for (int i = 1; i <= h; i++){
            for (int j = 1; j <= w; j++){
                cin >> field[j][i];
                if (field[j][i] == '@'){
                    sx = j; sy = i;
                }
            }
        }

        int ans;
        ans = dfs(sx, sy);
        cout << ans << endl;
        
    }
    

}