Go: package main

import (
	"bufio"
	"encoding/json"
	"fmt"
	"os"
	"strconv"
	"strings"
)

var (
	sc = bufio.NewScanner(os.Stdin)
)

type Color int

const (
	ColorBlack Color = iota
	ColorRed
)

var strByColor = map[Color]string{
	ColorBlack: "black",
	ColorRed:   "red",
}

func (c Color) String() string {
	return strByColor[c]
}

type Node struct {
	ID      int
	X, Y    int
	Color   Color
	NextIDs map[int]struct{}
}

func (n *Node) String() string {
	d, _ := json.Marshal(n)
	return string(d)
}

type Map struct {
	Width, Height int
	Nodes         map[int]*Node
}

func (m *Map) GetByID(id int) *Node {
	return m.Nodes[id]
}

func (m *Map) Get(x, y int) *Node {
	return m.Nodes[m.getID(x, y)]
}

func (m *Map) SetColor(x, y int, c Color) {
	m.Nodes[m.getID(x, y)].Color = c
}

func (m *Map) getID(x, y int) int {
	return x + y*m.Width
}

func (m *Map) init() {
	for x := 1; x <= m.Width; x++ {
		for y := 1; y <= m.Height; y++ {
			id := m.getID(x, y)
			m.Nodes[id] = &Node{ID: id, X: x, Y: y}
		}
	}
	for x := 1; x <= m.Width; x++ {
		for y := 1; y <= m.Height; y++ {
			nextIDs := map[int]struct{}{}
			if x > 1 {
				nextIDs[m.getID(x-1, y)] = struct{}{}
			}
			if x < m.Width {
				nextIDs[m.getID(x+1, y)] = struct{}{}
			}
			if y > 1 {
				nextIDs[m.getID(x, y-1)] = struct{}{}
			}
			if y < m.Height {
				nextIDs[m.getID(x, y+1)] = struct{}{}
			}
			m.Get(x, y).NextIDs = nextIDs
		}
	}
}

func NewMap(w, h int) *Map {
	m := &Map{Width: w, Height: h, Nodes: map[int]*Node{}}
	m.init()
	return m
}

type Searcher struct {
	Map        *Map
	queue      []*Node
	touchedIDs map[int]struct{}
	visitedIDs map[int]struct{}
}

func NewSearcher(m *Map) *Searcher {
	return &Searcher{
		Map:        m,
		queue:      []*Node{},
		touchedIDs: map[int]struct{}{},
		visitedIDs: map[int]struct{}{},
	}
}

func (s *Searcher) Search(start *Node) {
	s.enqueue(start)

	for {
		if len(s.queue) == 0 {
			break
		}
		for nextID := range s.dequeue().NextIDs {
			n := s.Map.GetByID(nextID)
			if n.Color == ColorRed || s.hasTouched(n) {
				continue
			}
			s.enqueue(n)
		}
	}
}

func (s *Searcher) VisitedNodeCount() int {
	return len(s.visitedIDs)
}

func (s *Searcher) hasTouched(n *Node) bool {
	_, ok := s.touchedIDs[n.ID]
	return ok
}

func (s *Searcher) enqueue(n *Node) {
	s.queue = append(s.queue, n)
	s.touchedIDs[n.ID] = struct{}{}
}

func (s *Searcher) dequeue() *Node {
	n := s.queue[0]
	s.queue = s.queue[1:]
	s.visitedIDs[n.ID] = struct{}{}
	return n
}

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])

		m := NewMap(w, h)

		// Set colors
		var start *Node
		for y := 1; y <= h; y++ {
			sc.Scan()
			for i, c := range sc.Text() {
				switch c {
				case '.', '@':
					m.SetColor(i+1, y, ColorBlack)
					if c == '@' {
						start = m.Get(i+1, y)
					}
				case '#':
					m.SetColor(i+1, y, ColorRed)
				}
			}
		}

		// Search
		s := NewSearcher(m)
		s.Search(start)
		fmt.Println(s.VisitedNodeCount())
	}
}

C++: #include <bits/stdc++.h>
using namespace	std;
static int dx[4]={-1,0,1,0},dy[4]={0,1,0,-1};
int h,w,r;
string s[20];
void dfs(int y,int x){
  r++;
  s[y][x]='#';
  for(int i=0;i<4;i++)
      if(0<=y+dy[i]&&y+dy[i]<h&&0<=x+dx[i]&&x+dx[i]<w)
	if(s[y+dy[i]][x+dx[i]]=='.') dfs(y+dy[i],x+dx[i]);
}
int main(){

  int y,x;
  for(;cin>>w>>h,w;){
  r=0;
  for(int i=0;i<h;i++) cin>>s[i];
  for(int i=0;i<h;i++) for(int j=0;j<w;j++) if(s[i][j]=='@') y=i,x=j;
  dfs(y,x);
  cout<<r<<endl;
  }
  return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <functional>
using namespace std;
#define MOD 1000000007
#define ADD(X,Y) ((X) = ((X) + (Y)%MOD) % MOD)
typedef long long i64; typedef vector<int> ivec; typedef vector<string> svec; typedef pair<int, int> pi;
int dd[] = { 0, 1, 0, -1 };


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

		char C[30][30];
		int B[30][30];

		int sx = -1; int sy = -1;
		for (int i = 0; i < H; i++)
		{
			for (int j = 0; j < W; j++)
			{
				cin >> C[i][j];
				B[i][j] = 0;
				if (C[i][j] == '@')
				{
					sy = i;
					sx = j;
				}
			}
		}

		queue<pi> Q;
		Q.push(pi(sy, sx));
		B[sy][sx] = 1;
		int ans = 1;
		while (!Q.empty())
		{
			int ty = Q.front().first; int tx = Q.front().second;
			Q.pop();

			for (int r = 0; r < 4; r++)
			{
				int y = ty + dd[r];
				int x = tx + dd[r + 1];
				if (y < 0 || y >= H || x < 0 || x >= W)continue;
				if (C[y][x] == '#')continue;
				if (B[y][x])continue;
				ans++;
				B[y][x] = 1;
				Q.push(pi(y, x));
			}
		}

		cout << ans << endl;
	}
	return 0;
}

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

#define REP(i,n) for(int i=0;i<(n);i++)

using namespace std;

char field[20][20];
int w, h;
int cnt = 0;

int dfs(int x, int y){
    field[x][y] = '#';
    cnt++;

    for(int dx=-1; dx<=1; dx++){
        for(int dy=-1; dy<=1; dy++){
            if(dx!=0 && dy!=0) continue;
            int nx = x + dx;
            int ny = y + dy;
            if(0 <= nx && nx < w && 0 <= ny && ny < h && field[nx][ny] == '.') dfs(nx,ny);
        }
    }


}

int main(){
    while(cin >> w >> h){
        if(w==0 && h==0) break;
        char line[w];
        int start_x, start_y;
        REP(j,h){
            cin >> line;
            REP(i,w){
                if(line[i] == '@'){
                    start_x = i;
                    start_y = j;
                    field[i][j] = '.';
                }
                field[i][j] = line[i];
            }
        }
        cnt = 0;
        dfs(start_x, start_y);
        cout << cnt << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <queue>
#include <stack>
#include <vector>
#include <stdio.h>
#include <string.h>
using namespace std;

int x[100][100]={0};
int count;

void foo(int s,int t){
	if(x[s][t]==0){
	}
	else{
		count++;
		x[s][t]=0;
		if(t-1>=0) foo(s,t-1);
		foo(s,t+1);
		if(s-1>=0) foo(s-1,t);
		foo(s+1,t);
	}
}
	
int main(){

	int w,h;
	int i,j;
	char tmp;
	int pos1,pos2;
	
	cin>>w>>h;
	while(!(w==0&&h==0)){
		memset(x,0,sizeof(x));
		count=0;
	for(i=0;i<h;i++){
		for(j=0;j<w;j++){
			cin>>tmp;
			//printf("%c\n",tmp);
			if(tmp=='.'){
				x[i][j]=1;
			}
			else if(tmp=='#'){
				x[i][j]=0;
			}
			else if(tmp=='@'){
				pos1=i;
				pos2=j;
				x[i][j]=1;
				//cout<<"pos 1 2  "<<pos1<<" "<<pos2<<endl;
			}
		}
		//cout<<endl;
	}
		//printf("hoge");
		
		/*for(i=0;i<h;i++){
			for(j=0;j<w;j++){
				cout<<x[i][j]<<" ";
			}
			cout<<endl;
		}
		cout<<endl;
		*/
		foo(pos1,pos2);
		//cout<<"hoge";
		cout<<count<<endl;
		cin>>w>>h;
		
	}
	
	
	return 0;
}

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

int W, H;
char v[30][30];
int sum;
int  dfs(int w, int h){
    int sum = 0;
    if(0<=w && w<W && 0<=h && h<H){
    if(v[w][h]=='.'){
        v[w][h] = '!';
        return 1;
    }
    sum += dfs(w+1, h);
    sum +=dfs(w-1, h);
    sum +=dfs(w, h+1);
    sum +=dfs(w, h-1);
    }
    return sum;
}

int main(void){
    string str;
    while(cin >> W >> H){
        v[30][30];
        if(W == 0 && H == 0)    break;
        for(int i=0; i<H; i++){
            cin >> str;
            for(int j=0; j<W; j++){
                v[i][j] = str[j];
                if(v[i][j] == '@')
                    dfs(i, j);
            }
        }
        cout << sum <<endl;
    }
    
    return 0;
}