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 <cstdio>

using namespace std;

#define MH 20
#define MW 20

char F[MH][MW];

int W, H;
bool input() {
    scanf("%d %d", &W, &H);
    if (W == 0 && H == 0) return false;
    for (int i = 0; i < H; i++) {
        scanf("%s", F[i]);
    }
    return true;
}

int dfs(int y, int x) {
    static const int dy[] = {0, 1, 0, -1},
                     dx[] = {1, 0, -1, 0};
    int count = 1;
    for (int i = 0; i < 4; i++) {
        int ny = y + dy[i],
            nx = x + dx[i];
        if (ny < 0 || ny >= H) continue;
        if (nx < 0 || nx >= W) continue;
        if (F[ny][nx] == '.') {
            F[ny][nx] = '@';
            count += dfs(ny, nx);
        }
    }
    return count;
}

void solve() {
    for (int y = 0; y < H; y++) {
        for (int x = 0; x < W; x++) {
            if (F[y][x] == '@') {
                printf("%d\n", dfs(y, x));
                return;
            }
        }
    }
}

int main() {
    while (input()) {
        solve();
    }
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

int main(){
	while(1){
		int W, H, x[30][30] = {};
		char str[30][30];
		cin>>W>>H;
		if(W==0 && H==0) break;
		for(int i = 0; i < W; i++){
			for(int j = 0; j < H; j++){
				cin>>str[i][j];
				if(str[i][j] == '@') x[i][j] = 1;
			}
		}
	
		int q = 0;
		while(1){
			int z = 0;
			for(int i = 0; i < W; i++){
				for(int j = 0; j < H; j++){
					if(x[i][j] == 1){
						if(i > 0 && str[i - 1][j] == '.') x[i - 1][j] = 1;
						if(i < W - 1  && str[i + 1][j] == '.') x[i + 1][j] = 1;
						if(j > 0 && str[i][j - 1] == '.') x[i][j - 1] = 1;
						if(j < H - 1&& str[i][j + 1] == '.') x[i][j + 1] = 1;
					}
				}
			}
			for(int i = 0; i < W; i++){
				for(int j = 0; j < H; j++){
					if(x[i][j] == 1) z++;
				}
			}
			if(z == q) break;
			q = z;
		}
		
		cout<<q<<endl;
	}
	return 0;
}

C++: #include <stdio.h>
#include <stdlib.h>
#include <iostream>

#define BLACK 0
#define RED 1
#define MAN 2

int count;
int tile[20][20];
int dx[] = {0,0,-1,1};
int dy[] = {-1,1,0,0};
int W,H;
int countdebug;

void hukasa(int width,int height);


int main(){

	int height,width;
	int i,j;
	char s;

	while(scanf("%d %d",&W,&H) && W && H){

		count = 0;


		for(j=0; j<H; j++){
			scanf("%*c");
			for(i=0; i<W; i++){

				scanf("%c",&s);

				if(s == '.'){
					tile[i][j] = BLACK;
				}
				else if(s == '#'){
					tile[i][j] = RED;
				}
				else if(s == '@'){
					tile[i][j] = RED;
					height = j;
					width = i;
				}

			}
		}

		hukasa(width,height);

		printf("%d\n",count+1);

	}
	return 0;
}



void hukasa(int width,int height){

	int i;


	for(i=0;i<4;i++){

		if(!(width + dx[i] < 0 || height + dy[i] < 0 || width + dx[i] > W - 1 || height + dy[i] > H - 1) ){
			if(tile[width + dx[i]][height + dy[i]] == BLACK){
				tile[width + dx[i]][height + dy[i]] = RED;
				count++;
				hukasa(width + dx[i],height + dy[i]);
			}
		}

	}
}

C++: #include <bits/stdc++.h>

using namespace std;

long long INF=1e15;

int n,m;
char field[30][30];

void dfs(int x,int y){
    //今いる場所を書き換え
    field[y][x]='1';

    //移動を8ループ
    for(int dx=-1;dx<=1;dx++){
        for(int dy=-1;dy<=1;dy++){

            if(dx*dy!=0)continue;

            int nx=x+dx,ny=y+dy;

            if(0<=nx && nx<n && 0<=ny && ny<m && field[ny][nx]=='.')dfs(nx,ny);
        }
    }
    return ;
}

signed main(){
    ios::sync_with_stdio(false);
    cin.tie(0);

    while(1){
        cin>>n>>m;
        
        if(n==0&&m==0)break;

        int sx,sy;

        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                cin>>field[i][j];
                if(field[i][j]=='@'){
                    sx=j;sy=i;
                }
            }
        }

        dfs(sx,sy);

        int res=0;

        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                if(field[i][j]=='1')res++;
            }
        }

        cout<<res<<endl;

    }
}

C++: #include <iostream>
#include <queue>
#include <map>

using namespace std;

typedef pair<int,int> P;
typedef queue<P> Q;

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

#define mp make_pair

int w,h;
char fie[21][21];

void bfs(int x, int y){
    Q q;
    q.push(mp(x,y));
    while(!q.empty()){
        for(int i=0; i<4; i++){
            int xx = q.front().first + dx[i];
            int yy = q.front().second + dy[i];
            if(0 <= xx && xx < w && 0 <= yy && yy < h && fie[yy][xx] == '.'){
                fie[yy][xx] = '@';
                q.push(mp(xx,yy));
            }
        }
        q.pop();
    }
}

int main(){
    while(cin >> w >> h , w||h){
        int sx,sy;
        for(int i=0; i<h; i++){
            cin >> fie[i];
            for(int j=0; j<w; j++){
                if(fie[i][j] == '@'){
                    sx = j; sy = i;
                }
            }
        }
        bfs(sx,sy);
        int ans = 0;
        for(int i=0; i<h; i++){
            for(int j=0; j<w; j++){
                if(fie[i][j] == '@') ans++;
            }
        }
        cout << ans << endl;
    }
}

C++: #include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);i++)
#define nrep(i,n) for(int i=1;i<=(n);i++)
#define FST first
#define SEC second
using namespace std;

typedef pair <int,int> pxy;
#define WMAX 20
#define HMAX 20
int dd[5]={0,1,0,-1,0};
int W,H;

void print(char map[HMAX][WMAX]){
  putchar('\n');
  rep(i,H){
    rep(j,W){
      cout << map[i][j];
    }
    putchar('\n');
  }
}

int dfs(char map[HMAX][WMAX]){
  stack <pxy> s;
  int n=0;
  rep(i,H){
    if(n) break;
    rep(j,W){
      if(map[i][j]=='@'){
	s.push(pxy(j,i));
	n=1;
	break;
      }
    }
  }

  while(!s.empty()){
    int cx=s.top().FST, cy=s.top().SEC;
    s.pop();
    if(map[cy][cx]=='.')
      n++;
    map[cy][cx]='#';
    rep(r,4){
      int nx=cx+dd[r], ny=cy+dd[r+1];
      if(nx<0||W<=nx||ny<0||H<=ny||map[ny][nx]=='#')
	continue;
      s.push(pxy(nx,ny));
    }
  }
  return n;
}


int main(){
  for(;;){
    scanf("%d %d",&W,&H);
    if(!(W+H)) break;
    
    char map[HMAX][WMAX];
    rep(i,H){
      string s;
      cin >> s;
      strcpy(map[i],s.c_str());
    }
    printf("%d\n",dfs(map));
  }
}