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 <algorithm>

#define range(i,a,b) for(int (i)=a;(i)<(b);(i)++)
#define rep(i,n) range(i,0,n)

using namespace std;

char table[30][30];

int dw[4]={1,0,-1,0};
int dh[4]={0,1,0,-1};

void dfs(int w,int h){
	table[h][w]='@';
	rep(i,4){
		int nw=w+dw[i];
		int nh=h+dh[i];
		if(table[nh][nw]=='.')
			dfs(nw,nh);
	}
}

int main(void){
	int w,h;
	while(cin >> w >> h,w|h){
		int sw,sh;
		rep(i,30)rep(j,30) table[i][j]='#';
		range(i,1,h+1) range(j,1,w+1){
			cin >> table[i][j];
			if(table[i][j]=='@'){
				sh=i;
				sw=j;
			}
		}
		dfs(sw,sh);
		int ans=0;
		range(i,1,h+1) range(j,1,w+1) if(table[i][j]=='@') ans++;
		cout << ans << endl;
	}
	return 0;
}

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

#define rep(i,n) rep2(i,0,n)
#define rep2(i,m,n) for(int i=m;i<n;i++)

int w,h,ans,dy[]={-1,0,1,0},dx[]={0,-1,0,1};
char c[22][22];

void dfs(int y,int x){
	ans++;
	c[y][x]='#';
	rep(i,4){
		int ny=y+dy[i],nx=x+dx[i];
		if(c[ny][nx]=='-')dfs(ny,nx);
	}
}

int main(){
	while(cin>>w>>h&&w){
		ans=0;
		int y,x;
		rep2(i,1,h+1)rep2(j,1,w+1){
			cin>>c[i][j];
			if(c[i][j]=='@')y=i,x=j;
		}
		dfs(y,x);
		cout<<ans<<endl;
	}
}

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

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

void bfs(vector< vector<char> > &plane, int x, int y, int &ans){  
  plane[x][y] = '#';
  ans++;
  for(int i=0; i<4; i++){
    if(0 <= x+dx[i] && x+dx[i] < w && 0 <= y+dy[i] && y+dy[i] < h)
      if(plane[x + dx[i]][y + dy[i]] != '#')
        bfs(plane, x + dx[i], y + dy[i], ans);
  }
  
  return;
}

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

    int sx, sy;
    vector< vector<char> > plane(w, vector<char>(h));
    for(int i=0; i<h; i++){
      for(int j=0; j<w; j++){
        cin >> plane[j][i];
        if(plane[j][i] == '@'){
          sx = j;
          sy = i;
        }
      }
    }

    int ans = 0;
    bfs(plane, sx, sy, ans);
    cout << ans << endl;
  }
  
  return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
int main(){
  int w,h,a[20][20],str1,str2,count=0,m;
  char in;
  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>>in;
	if(in=='#') a[i][j]=0;
	else if(in=='@') {
	  a[i][j]=2;
	}
	else a[i][j]=1;
      }
    }
    count=0;
    while(1){
      m=0;
      for(int i=0;i<h;i++){
	for(int j=0;j<w;j++){
	  if(a[i][j]==2){
	    m=1;
	    count++;
	    a[i][j]=3;
	    if(i==0){
	      if(j==0){
		if(a[i+1][j]==1) a[i+1][j]=2;
		if(a[i][j+1]==1) a[i][j+1]=2;
	      }
	      else {
		if(a[i][j-1]==1) a[i][j-1]=2;
		if(a[i+1][j]==1) a[i+1][j]=2;
		if(a[i][j+1]==1) a[i][j+1]=2;
	      }
	    }
	    else if(j==0){
		if(a[i-1][j]==1) a[i-1][j]=2;
		if(a[i+1][j]==1) a[i+1][j]=2;
		if(a[i][j+1]==1) a[i][j+1]=2;
	    }
	    else if(i==h-1){
	      if(j==w-1){
		if(a[i-1][j]==1) a[i-1][j]=2;
		if(a[i][j-1]==1) a[i][j-1]=2;
	      }
	      else {
		if(a[i][j+1]==1) a[i][j+1]=2;
		if(a[i-1][j]==1) a[i-1][j]=2;
		if(a[i][j-1]==1) a[i][j-1]=2;
	      }
	    }
	    else if(j==w-1){
		if(a[i+1][j]==1) a[i+1][j]=2;
		if(a[i-1][j]==1) a[i-1][j]=2;
		if(a[i][j-1]==1) a[i][j-1]=2;
	    }
	    else {
		if(a[i+1][j]==1) a[i+1][j]=2;
		if(a[i-1][j]==1) a[i-1][j]=2;
		if(a[i][j-1]==1) a[i][j-1]=2;
		if(a[i][j+1]==1) a[i][j+1]=2;
	    }
	  }
	}
      }
      if(m==0) break;
    }
    cout<<count<<endl;
  }
    
    
  return 0;
}

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

typedef pair<int, int> P;

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

int main()
{
	char map[32][32];
	queue< P > que;
	while (true)
	{
		int w, h, x, y;
		cin >> w >> h;
		if (!(w || h)) break;
		for (int i = 0; i < h; i++)
		{
			cin >> map[i];
			char* x0 = index(map[i], '@');
			if (x0 != NULL)
			{
				x = x0 - map[i];
				y = i;
			}
		}
		int count = 0;
		que.push(P(x, y));
		map[y][x] = '#';
		while (!que.empty())
		{
			P current = que.front();
			que.pop();
			count++;
			for (int i = 0; i < 4; i++)
			{
				int nx = current.first + dx[i];
				int ny = current.second + dy[i];
				if ((0 <= nx && nx < w && 0 <= ny && ny < h) && (map[ny][nx] == '.'))
				{
					que.push(P(nx, ny));
					map[ny][nx] = '#';
				}
			}
		}
		cout << count << endl;
	}
	return 0;
}

C++: #include<iostream>

using namespace std;

const int maxSize = 21;
int mapData[maxSize][maxSize] = {0};
int W, H, Ans;

void dfs(int hh, int ww) {
  if(mapData[hh][ww] == 1) {
    mapData[hh][ww] = 0;
    Ans++;
    if(hh+1<H && mapData[hh+1][ww]==1) {
      dfs(hh+1, ww);
    }
    if(ww+1<W && mapData[hh][ww+1]==1) {
      dfs(hh, ww+1);
    }
    if(0<=hh-1 && mapData[hh-1][ww]==1) {
      dfs(hh-1, ww);
    }
    if(0<=ww-1 && mapData[hh][ww-1]==1) {
      dfs(hh, ww-1);
    }
  }
}

int main() {
  while(cin>>W>>H && !(W==0 && H==0)) {
    int startW, startH;
    Ans = 0;
    for(int i=0; i<H; i++) {
      string str;
      cin>>str;
      for(int j=0; j<W; j++) {
	if(str[j] == '.') {
	  mapData[i][j] = 1; // true
	}
	else if(str[j] == '#') {
	  mapData[i][j] = -1; // false;
	}
	else {
	  mapData[i][j] = 1; //true
	  startW = i;
	  startH = j;
	}
      }
    }
    /*
    for(int i=0; i<H; i++) {
      for(int j=0; j<W; j++) {
	cout<<mapData[i][j]<<" ";
      }
      cout<<endl;
    }
    */
    dfs(startW, startH);
    /*
    for(int i=0; i<H; i++) {
      for(int j=0; j<W; j++) {
	cout<<mapData[i][j]<<" ";
      }
      cout<<endl;
    }
    */
    cout<<Ans<<endl;
  }
}