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 <queue>

using namespace std;

struct locate{
  int x;
  int y;
};
 
char graph[20][20];
int cou = 0;
int H,W;

void bfs(locate z){
  queue<locate> Q;
  locate u;
  locate v;
  Q.push(z);
 

  while(!Q.empty()){

    u = Q.front();Q.pop();

    if(graph[u.y + 1][u.x] == '.' && graph[u.y + 1][u.x] != 'N'){
      graph[u.y + 1][u.x] = 'N';
      cou++;
      v.y = u.y + 1;
      v.x = u.x;
      Q.push(v);
    }

    if(graph[u.y][u.x + 1] == '.' && graph[u.y][u.x + 1] != 'N'){
      graph[u.y][u.x + 1] = 'N';
      cou++;
      v.x  = u.x + 1;
      v.y = u.y;
      Q.push(v);
    }

    if(graph[u.y - 1][u.x] == '.' && graph[u.y - 1][u.x] != 'N'){
      graph[u.y - 1][u.x] = 'N';
      cou++;
      v.x = u.x;
      v.y = u.y - 1;
      Q.push(v);
    }

    if(graph[u.y][u.x - 1] == '.' && graph[u.y][u.x - 1] != 'N'){
      graph[u.y][u.x - 1] = 'N';
      cou++;
      v.x = u.x - 1;
      v.y = u.y;
      Q.push(v);
    }
    
  }
  cout << endl;
    for(int i = 0; i< H ;i++){
      for(int j = 0; j < W; j++){
	cout << graph[i][j];
      }
      cout << endl;
      }
}

int main(){

  int a1,a2;
  locate a;
  while(1){

    cin >> W >> H;

    if(W == 0 && H == 0) break; 


    for(int i = 0; i< H ;i++){
      for(int j = 0; j < W; j++){
	cin >> graph[i][j];
	if(graph[i][j] == '@'){
	  a1 = i;
	  a2 = j;
	}
      }
    }

    /*
      for(int i = 0; i< H ;i++){
      for(int j = 0; j < W; j++){
      cout << graph[i][j];
      }
      cout << endl;
      }
    */

    a.y = a1;
    a.x = a2;
    bfs(a);

    cout << cou+1 << endl;

    cou = 0;
    for(int i = 0;i < H ;i++){
      for(int j = 0;j < W; j++){
	graph[i][j] = 'N';
      }
    }
    cou = 0;
  }
  return 0;
}

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

int tansaku(char tile[20][20],int w1,int h1){
    if(tile[w1][h1]!='.'&&tile[w1][h1]!='@')return 0;
    tile[w1][h1]='t';
    return 1+tansaku(tile,w1+1,h1)+tansaku(tile,w1-1,h1)+tansaku(tile,w1,h1+1)+tansaku(tile,w1,h1-1);
}

int main(){
    int w,h;
    int w1,h1; //スタート地点
   // 標準入力
   while(1){
    std::cin >> w;
    std::cin >> h;
    if(w==0&&h==0)break;
   // 配列の初期化.
    char tile[20][20];
    for(int i=0; i<h; i++){
        for(int j=0; j<w; j++){
            std::cin >> tile[j][i];
            if(tile[j][i]=='@'){
                w1=j; h1=i;
            }
        }
    }
    std::cout << tansaku(tile,w1,h1) << std::endl;
   }

    return 0;
}

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


int main(){
    std::vector<int> row;
    int prev_col, width, height, max = 0, last = 0;
    bool connect_prev_row;
    
    std::cin >> width >> height;
    row.resize(width+1);
    for( int i = 0; i <= width; i++ ) row[i] = 0;

    std::string line;
    while( true ){
        std::cin >> line;
        if( line == "00" ) {
            std::cout << max;
            break;
        }
        connect_prev_row = false;
        for(std::string::size_type i = 0; i < line.size(); i++ ){
            if( line[i] == '.' ){
                if( connect_prev_row ){
                    if( row[i] > 0 ) row[i+1] = row[i] + 1;
                    else row[i+1] = row[i] - 1;
                } else {
                    connect_prev_row = true;
                    if( row[i] <= 0 && row[i+1] <= 0 ) row[i+1] = row[i+1] + row[i] - 1;
                    else row[i+1] = std::abs(row[i+1]) + std::abs(row[i]) + 1;
                }
            } else if( line[i] == '@' ) {
                if ( connect_prev_row ) row[i+1] = - row[i] + 1;
                else {
                    connect_prev_row = true;
                    row[i+1] = - row[i+1] - row[i] + 1;
                }
            } else {
                row[i+1] = 0;
                connect_prev_row = false;
            }
            max = max > row[i+1] ? max : row[i+1];
        }
        last = 0;
        for( int i = line.size(); i > 0; i-- ) {
            if( row[i] == 0 ) last = 0;
            else if( row[i] > 0 ){
                if(  last == 0 ) last = row[i];
                else row[i] = last;
            } else {
                if(  last == 0 ) last = row[i];
                else row[i] = last;
            } 
        }
    }
    return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<vector>
#include<map>
#include<queue>
using namespace std;
#define REP(i, a, n) for(int i=a; i<n; i++)
#define INF 1000000000


int dy[4] = { -1, 0, 1, 0 };
int dx[4] = { 0, 1, 0, -1 };

int main() {
	int W, H;
	while (cin >> W >> H, W || H) {
		int fy, fx;
		char field[21][21];
		bool visit[21][21] = {};
		REP(i, 0, H) REP(j, 0, W) {
			cin >> field[i][j];
			if (field[i][j] == '@') {
				fy = i;
				fx = j;
				visit[i][j] = true;
			}
		}

		queue<pair<int, int>> q;
		pair<int, int> pii;
		q.push(make_pair(fy, fx));
		visit[fy][fx] = true;

		while (!q.empty()) {
			pii = q.front();
			q.pop();

			REP(k, 0, 4) {
				int y = pii.first + dy[k];
				int x = pii.second + dx[k];
				if (y < 0 || x < 0 || y >= H || x >= W) continue;
				if (field[y][x] == '#' || visit[y][x]) continue;

				visit[y][x] = true;
				q.push(make_pair(y, x));
			}
		}

		int ans = 0;
		REP(i, 0, H) {
			REP(j, 0, W) {
				if (visit[i][j]) ans++;
			}
		}
		cout << ans << endl;
	}
	return 0;
}

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

using namespace std;

int h, w, sy, sx, dy[] = {-1, 0, 1, 0}, dx[] = {0, 1, 0, -1};
char data[20][20];
bool vis[20][20];

bool check(int y, int x){
  if(y<0 || y>=h) return false;
  if(x<0 || x>=w) return false;
  return true;
}

int dfs(int y, int x){
  int res = 1;
  vis[y][x] = true;
  for(int i=0;i<4;i++){
    int ny = y + dy[i];
    int nx = x + dx[i];
    if(!check(ny, nx)) continue;
    if(vis[ny][nx]) continue;
    if(data[ny][nx] == '.') res += dfs(ny, nx);
  }
  return res;
}

main(){
  while(cin >> w >> h && (w|h)){
    fill(vis[0], vis[20], false);
    for(int i=0;i<h;i++){
      for(int j=0;j<w;j++){
        cin >> data[i][j];
        if(data[i][j] == '@'){
          sy = i;
          sx = j;
          data[i][j] = '.';
        }
      }
    }
    cout << dfs(sy, sx) << endl;
  }
}