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 <stdio.h>
int A[4][2]={-1,0,0,1,1,0,0,-1},ans,N,M;char RB[25][25];void bfs(int x, int y) {RB[x][y]='#';ans++;for (int i=0;i<4;i++) {int nx=x+A[i][0],ny=y+A[i][1];if (nx>=0 && nx<N && ny>=0 && ny<M && RB[nx][ny]=='.') bfs(nx,ny);}}
int main() {int i,j;while (1) {scanf("%d %d",&M,&N);if (!N && !M) return 0;for (i=0;i<N;scanf("%s",&RB[i++]));ans=0;for (i=0;i<N;i++) for (j=0;j<M;j++) if (RB[i][j]=='@') bfs(i,j);printf("%d\n",ans);}}

C++: #include<iostream>
#include<algorithm>
#include<queue>
#include<cstring>
using namespace std;
char cm[200][200];
int im[200][200];
 int W,H;
bool visited[200][200];
int sy,sx;
int dx[4] = {1,0,-1,0};
int dy[4] = {0,1,0,-1};
typedef pair<int,int> P;
int maxx = 1;
int q = 1;

int dp(int x,int y){
 

  for(int i=0;i<4;i++)
    {
      int ny = y+dy[i],nx = x + dx[i];
      if(0 <= nx && nx < W && 0 <= ny && ny < H && cm[ny][nx] != '#' && !visited[ny][nx]){
	q++;
	im[ny][nx] = q;
	maxx = max(maxx,q);
	visited[ny][nx] = true;
	dp(nx,ny);
      }
    }
}


int main(){
 

  while(1)
    {
      cin >> W >> H;
      if(W == 0 && H == 0)break;
      maxx = 1;
      memset(im,0,sizeof(im));
      memset(visited,false,sizeof(visited));
      for(int i=0;i<H;i++)
	{
	  for(int j=0;j<W;j++)
	    {
	      cin >> cm[i][j];
	      if(cm[i][j] == '#'){
		im[i][j] = 0;
	      }
	      else if(cm[i][j] == '@')
		{
		  sy = i;
		  sx = j;
		}
	    }
	}

      im[sy][sx]=1;
      q = 1;
      visited[sy][sx] = true;
      dp(sx,sy);
      cout << maxx  << endl;
      /*          
 for(int i=0;i<H;i++){
	for(int j=0;j<W;j++)cout << im[i][j];
	cout << endl;
      }
      */

    }
}

C++: #include<iostream>
#include<vector>
#include<queue>
#include<utility>
using namespace std;
int w,h;
string matrix[20];

const int dx[]={1,0,-1,0}, dy[]={0,-1,0,1};
bool valid(int x,int y)
{
    return (x>=0)&&(x<w)&&(y>=0)&&(y<h)&&(matrix[y][x]!='#');
}
int main()
{
    while(true)
    {
        queue<pair<int,int> > q;
        pair<int,int> man;
        int amount=1;
        
        cin>>w>>h;
        if(w==0&&h==0)
            break;
        for(int i=0;i<h;i++)
        {
            cin>>matrix[i];
            cout<<matrix[i]<<endl;
        }
        
        for(int i=0;i<h;i++)
        {
            for(int j=0;j<w;j++)
            {
                if(matrix[i][j]=='@')
                {
                    man.first=j;
                    man.second=i;
                }
            }
        }
        
        q.push(man);
        while(!q.empty())
        {
            pair<int,int> current;
            current=q.front();
            q.pop();
            
            for(int i=0;i<4;i++)
            {

                if(valid(current.first+dx[i],current.second+dy[i]))
                {
                    q.push(make_pair(current.first+dx[i],current.second+dy[i]));
                    matrix[current.second+dy[i]][current.first+dx[i]]='#';
                    amount++;
                    //cout<<current.first+dx[i]<<","<<current.second+dy[i]<<endl;
                }
            }
            
            matrix[current.second][current.first]='#';
        }
        
        cout<<amount<<endl;
    }
}

C++: //??¨??¢?´¢:??±???????????¢?´¢??????????????¢?´¢ 

//??????????????¢?????¬?????????
 
//?????°??¢??°???????????????(?????????)????????\???(?????????)
#include <stdio.h>
#include <queue>
#include <string.h>
using namespace std;	
int W,H;
char c[101][101];
bool visited[100][100];
 
int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};
 	
void compute();//????????????????????£?¨? 
	
int main(){
	
	while(scanf("%d %d",&W,&H),W |H){
	    int i;
		
		for(i=0;i<H;i++){
			scanf("%d",&c[i][0]);
		}
	}
	return 0;
}

void compute(){
	
	memset(visited,false,sizeof visited);  //{????????????????????????1bit??????????????????1bit????????§?????????} 
	
	queue<int> que;
	int i,j;
	for(j=0;j<W;j++){ 
	 for(i=0;i<H;i++){
	  if(c[i][j]=='@'){
	  	que.push(j+i*H);
	  	visited[i][j]==true;
	  	 break;
	  }
	 }
	}
  int answer=1;
  while(!que.empty()){
	int cur=que.front();
	        que.pop();
	        int x=cur%W;
	        int y=cur/W;
    

  for(i=0;i<4;i++){
	int nx=x+dx[i],ny=y+dy[j];
	
  
  
  if(!(0<=nx&&nx<W&&0<=ny))continue;
  if(c[ny][nx]=='#'||visited[ny][nx])continue;

  que.push(nx+ny*W);
  visited[ny][nx]=true;

    }
   }
 
 }

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

int moved = 0;
int w, h;
char myMap[20][20];

bool safe(int x, int y){
    return (x < h && y < w) || (x >= 0 && y >= 0);
}

void move(int x, int y){
    myMap[x][y] = '#';
    moved++;
    if (myMap[x+1][y] == '.' && safe(x+1, y)) move(x+1, y);
    if (myMap[x-1][y] == '.' && safe(x-1, y)) move(x-1, y);
    if (myMap[x][y+1] == '.' && safe(x, y+1)) move(x, y+1);
    if (myMap[x][y-1] == '.' && safe(x, y-1)) move(x, y-1);
    return;
}

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

	moved = 0;
	int initX, initY;

	for (int i = 0; i < h; i++){
	    for (int j = 0; j < w; j++){
		cin >> myMap[i][j];
		if (myMap[i][j] == '@'){
		    initX = i;
		    initY = j;
		}
	    }
	}
	
	move(initX, initY);
	
	cout << moved << endl;
    }
}