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 <vector>
#include <string>
using namespace std;

int explorer(vector<string> *map,int i, int j){
	if(map->at(i)[j]=='#') return 0;
	
	int cnt=1;
	vector<int>vi;
    vi.reserve(4);
	vector<int>vj;
    vj.reserve(4);
	
	map->at(i)[j]='#';
	
	if(i!=0&&map->at(i-1)[j]=='.'){
		vi.push_back(i-1);
		vj.push_back(j);
	}if(i+1!=map->size()&&map->at(i+1)[j]=='.'){
		vi.push_back(i+1);
		vj.push_back(j);		
	}if(j!=0&&map->at(i)[j-1]=='.'){
		vi.push_back(i);
		vj.push_back(j-1);		
	}if(j+1!=map->at(i).size()&&map->at(i)[j+1]=='.'){
		vi.push_back(i);
		vj.push_back(j+1);		
	}

	while(!vi.empty()){
    cout<<i<<j<<endl;
		cnt += explorer(map,vi.back(),vj.back());
		vi.pop_back();
		vj.pop_back();
	}

	return cnt;
}

int main() {
	int w,h;
	
	while(cin >> w >> h,w){
	vector<string> map;
	int psx=0,psy=0;
	map.resize(h);
	for(int i=0;i<h;i++){
		cin >> map[i];
		
		if(psx==0){
			if(map[i].find('@')!=-1){
				psx=map[i].find('@');
				psy=i;
			}
		}
	}
	
	cout << explorer(&map,psy,psx) << endl;
	}
	return 0;
}

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

using namespace std;

const int dm[] = {-1, 0, 1, 0}, dn[] = {0, -1, 0, 1};
int h, w, count;
vector< vector<int> > field;

bool valid(int m, int n) {
    return 0 <= m && m < h && 0 <= n && n < w && field[m][n] == 1;
}

void dfs(int m, int n) {
    field[m][n] = 0;
    count++;

    for(int i = 0; i < 4; i++) {
        if(valid(m + dm[i], n + dn[i])) {
            dfs(m + dm[i], n + dn[i]);
        }
    }
}

int main() {
    while(1) {
        cin >> w >> h;
        if (w == 0 && h == 0) {
            break;
        }

        field.resize(h);
        int m, n;
        for (int i = 0; i < h; i++) {
            string input;
            cin >> input;

            field[i].resize(w);

            for (int j = 0; j < w; j++) {
                if(input[j] == '@') {
                    m = i;
                    n = j;
                }
                if(input[j] == '#') {
                    field[i][j] = 0;
                } else {
                    field[i][j] = 1;
                }
            }
        }

        count = 0;
        dfs(m, n);

        cout << count << endl;
    }

    return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
int H,W;
char map[21][21];
int dist[21][21];
using namespace std;

void solve(){
  int nx,ny,sx,sy;
  const int dx[] = {1,0,-1,0};
  const int dy[] = {0,1,0,-1};
  for(int height = 0; height < H; height++){
    for(int width = 0; width < W ; width++){
      dist[height][width] = 0;
      if(map[height][width] == '@'){
        sx = width;
        sy = height;
      }
    }
  }

  dist[sy][sx] = 1;
  for(int d = 1; d < H * W; d++){
    for(int height = 0; height < H; height++){
      for(int width = 0; width < W ; width++){
        if(d == dist[height][width]){
          for(int dir = 0 ; dir < 4; dir++){
            nx = width + dx[dir];
            ny = height + dy[dir];
            if(nx >= 0 && nx < W && ny >= 0 && ny < H &&
               map[ny][nx] != '#' && dist[ny][nx] == 0){

              dist[ny][nx] = dist[height][width] + 1;

            }
          }
        }
      }
    }
  }
  int res = 0;
  for(int height = 0; height < H; height++){
    for(int width = 0; width < W ; width++){
      //cout << dist[height][width] ;
      if(dist[height][width] != 0) res++;
    }
    //cout << endl;
  }
  cout << res << endl;
}

int main(){
  while(true){
    cin >> W >> H ;
    if(W + H == 0) break;
    for(int height = 0; height < H; height++){
      for(int width = 0; width < W ; width++){
        cin >> map[height][width];
      }
    }
    solve();
  }
  return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
bool c[20][20] = {} ;
int cnt,w, h, p[20][20] = {};

int main() {
	int j, f,cx,cy;
	char in[20];
	while (1) {
		for (int i = 0; i < 400; i++) {
			c[i / 20][i % 20] = p[i / 20][i % 20] = 0;
		}
		cnt = 0;
		f = 1;
		scanf("%d %d", &w, &h);
		if (w ==0&& h == 0)
			break;
		scanf("\n", &j);
		for (int i = 0; i < h; i++) {
			scanf("%s", &in);
			for (j = 0; j < w; j++) {
				switch (in[j]) {
				case '#':
					c[j][i] = 0;
					p[j][i] = -1;
					break;
				case '@':
					cx = j;
					cy = i;
					p[j][i] = 1;
				case '.':
					c[j][i] = 1;
				}
			}
		}

		/*for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++)
				printf("%3d", c[j][i]);
			printf("\n");
		}*/

		while (f == 1) {
			f = 0;
			if (w != 1 && h != 1) {
				for (int i = 0; i < w*h; i++) {
					if (p[i / h][i%h] == 0 && (p[i / h + 1][i % h] == 1 || p[i / h - 1][i % h] == 1 || p[i / h][i % h + 1] == 1 || p[i / h][i % h - 1] == 1)) {
						p[i / h][i%h] = 1;
						f = 1;
					}
				}
			}
			if (w = 1 && h != 1) {
				for (int i = 0; i < w*h; i++) {
					if (p[i / h][i%h] == 0 && (p[i / h][i % h + 1] == 1 || p[i / h][i % h - 1] == 1)) {
						p[i / h][i%h] = 1;
						f = 1;
					}
				}
			}
			if (w != 1 && h = 1) {
				for (int i = 0; i < w*h; i++) {
					if (p[i / h][i%h] == 0 && (p[i / h + 1][i % h] == 1 || p[i / h - 1][i % h] == 1)) {
						p[i / h][i%h] = 1;
						f = 1;
					}
				}
			}


			/*for (int i = 0; i < h; i++) {
				for (int j = 0; j < w; j++)
					printf("%3d", p[j][i]);
				printf("\n");
			}
			printf("\n");*/
		}

		for (int i = 0; i < w*h; i++) {
			if (p[i / h][i%h] == 1)
				cnt++;
		}
		printf("%d\n", cnt);
	}
	return 0;
}