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>
using namespace std;

const int NUM = 7;

void grooping(int y, int x, int w, int h, char** room, unsigned long*** group, unsigned long* next)
{
	if (room[y][x] != '#') {
		for (int i = y - 1; i <= y + 1; i++) {
			for (int j = x - 1; j <= x + 1; j++) {
				if (i < 0 || j < 0 || i >= h || j >= w) {
					continue;
				}
				if ((i == y && j != x) || (i != y && j == x)) {
					for (int k = 0; k < NUM; k++) {
						group[y][x][k] |= group[i][j][k];
					}
				}
			}
		}
		for (int i = 0; i < NUM; i++) {
			if (group[y][x][i] == 0UL && next[i] != 0UL) {
				group[y][x][i] |= next[i];
				next[i] <<= 1;
				break;
			}
		}
	}
}

int main()
{
	int w, h;
	while (true) {
		cin >> w >> h;
		if (w == 0 && h == 0) {
			break;
		}

		unsigned long next[NUM] = { 1UL, 1UL, 1UL, 1UL, 1UL, 1UL, 1UL };
		char** room = new char*[h];
		unsigned long*** group = new unsigned long**[h];
		int x, y;
		for (int i = 0; i < h; i++) {
			room[i] = new char[w];
			group[i] = new unsigned long*[w];
			for (int j = 0; j < w; j++) {
				cin >> room[i][j];
				if (room[i][j] == '@') {
					x = j;
					y = i;
				}
				group[i][j] = new unsigned long[NUM];
				for (int k = 0; k < NUM; k++) {
					group[i][j][k] = 0UL;
				}
			}
		}

		for (int k = 0; k < 180; k++) {
			for (int i = 0; i < h; i++) {
				for (int j = 0; j < w; j++) {
					grooping(i, j, w, h, room, group, next);
				}
			}
			for (int i = h - 1; i >= 0; i--) {
				for (int j = w - 1; j >= 0; j--) {
					grooping(i, j, w, h, room, group, next);
				}
			}
			for (int j = 0; j < w; j++) {
				for (int i = 0; i < h; i++) {
					grooping(i, j, w, h, room, group, next);
				}
			}
			for (int j = w - 1; j >= 0; j--) {
				for (int i = h - 1; i >= 0; i--) {
					grooping(i, j, w, h, room, group, next);
				}
			}
		}

		int count = 0;
		for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++) {
				for (int k = 0; k < NUM; k++) {
					if ((group[i][j][k] & group[y][x][k]) != 0UL) {
						count++;
						break;
					}
				}
			}
		}

		cout << count << '\n';

		for (int i = 0; i < h; i++) {
			delete[] room[i];
			for (int j = 0; j < w; j++) {
				delete[] group[i][j];
			}
			delete[] group[i];
		}
		delete[] room;
		delete[] group;
	}

	return 0;
}

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

int main(){

char N[21][21]={};
char L[21]={};

int W,H;
while(1){
cin>>W>>H;if(W==0&&H==0)break;


for(int i=0;i<H;i++){
scanf("%s",L);
for(int j=0;j<W;j++)
N[i][j]=L[j];
}

int n[22][22]={};int c=0;
for(int i=1;i<H+1;i++)
for(int j=1;j<W+1;j++)
{if(n[i][j]==0&&(N[i-1][j-1]=='@'||N[i-1][j-1]=='.')){c++;
n[i][j]=c;}
if(N[i-1][j-1]=='@'||N[i-1][j-1]=='.'){
if(N[i-1][j+1-1]=='@'||N[i-1][j+1-1]=='.')n[i][j+1]=n[i][j];
if(N[i+1-1][j-1]=='@'||N[i+1-1][j-1]=='.')n[i+1][j]=n[i][j];
}
}

for(int i=0;i<H+1;i++)
for(int j=0;j<W+1;j++)
{if(n[i][j]!=0&&n[i][j+1]>n[i][j]){
int t=n[i][j+1];
for(int ii=0;ii<H+1;ii++)
for(int jj=0;jj<W+1;jj++)
if(n[ii][jj]==t)n[ii][jj]=n[i][j];
}
if(n[i][j]!=0&&n[i][j-1]>n[i][j]){
int t=n[i][j-1];
for(int ii=0;ii<H+1;ii++)
for(int jj=0;jj<W+1;jj++)
if(n[ii][jj]==t)n[ii][jj]=n[i][j];
}
if(n[i][j]!=0&&n[i+1][j]>n[i][j]){
int t=n[i+1][j];
for(int ii=0;ii<H+1;ii++)
for(int jj=0;jj<W+1;jj++)
if(n[ii][jj]==t)n[ii][jj]=n[i][j];
}
if(n[i][j]!=0&&n[i-1][j]>n[i][j]){
int t=n[i-1][j];
for(int ii=0;ii<H+1;ii++)
for(int jj=0;jj<W+1;jj++)
if(n[ii][jj]==t)n[ii][jj]=n[i][j];
}
}

int p=0;
for(int i=0;i<H;i++)
for(int j=0;j<W;j++)
if(N[i][j]=='@')p=n[i+1][j+1];
/*
for(int i=1;i<H+2;i++){
for(int j=1;j<W+2;j++)
	cout<<n[i][j];
cout<<endl;
}*/

int g=0;
for(int i=1;i<H+1;i++)
for(int j=1;j<W+1;j++)
if(n[i][j]==p)g++;

cout<<g<<endl;
}

return 0;
}

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

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

int dfs(int y, int x, vector<string> &g){
  if(g[y][x] == '#')return 0;
  g[y][x] = '#';

  int res = 1;
  for(int i=0;i<4;i++){
    int ny = y + dy[i], nx = x + dx[i];
    if(ny<0 || nx<0 || ny>=(int)g.size() || nx>=(int)g[0].size())continue;
    res += dfs(ny,nx,g);
  }
  return res;
}

int main(){
  int w,h;
  while(cin >> w >> h){
    if(w==0 && h==0)break;

    vector<string> g(h);
    int y=0,x=0;
    for(int i=0;i<h;i++){
      cin >> g[i];
      for(int j=0;j<w;j++){
	if(g[i][j] == '@')y = i, x = j;
      }
    }

    cout << dfs(y,x,g) << endl;
  }
}