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 <bits/stdc++.h>
using namespace std;

using ll = long long;
#define debug(x) cerr << #x << ": " << x << endl;
#define line() cerr << "---------------" << endl;

char board[30][30];
bool visited[30][30];

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

void dfs(int x, int y) {
   for (int i = 0; i < 4; i++) {
      int nx = x + dx[i], ny = y + dy[i];
      if (nx < 0 || nx >= H || ny < 0 || ny >= W) continue;
      if (board[nx][ny] == '#') continue;
      if (visited[nx][ny]) continue;
      visited[nx][ny] = true;
      dfs(nx, ny);
   }
}

int main() {
   while (cin >> W >> H, W || H) {
      memset(visited, false, sizeof(visited));

      int sx = 0, sy = 0; // 人の座標
      for (int i = 0; i < H; i++) {
         for (int j = 0; j < W; j++) {
            cin >> board[i][j];
            if (board[i][j] == '@') {
               sx = i, sy = j;
            }
         }
      }

      visited[sx][sy] = true;
      dfs(sx, sy);

      int ans = 0;
      for (int i = 0; i < H; i++) {
         for (int j = 0; j < W; j++) {
            if (visited[i][j]) ans++;
         }
      }
      cout << ans << endl;

   }

   return 0;
}

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

using namespace std;

int main(){
    int w,h;
    while(cin >> w >> h && w!=0){
        int t[w+2][h+2];
        int matrix[w*h][w*h];
        int start;
        for(int i=0;i<h;i++){
            for(int j=0;j<w;j++){
                if(i==0 || j==0 || i==w || j==h)
                    t[i][j]=0;
                char tmp; cin >> tmp;
                if(tmp=='.'){
                    t[i+1][j+1] = 1;
                }
                else if(tmp=='#'){
                    t[i+1][j+1] = 0;
                }
                else{
                    t[i+1][j+1] = 1;
                    start = i*w+j;
                }
                cin >> t[i+1][j+1];
            }
        }
        for(int i=0;i<w*h;i++){
            for(int j=0;j<w*h;j++){
                matrix[i][j] = 0;
            }
        }
        for(int i=0;i<h;i++){
            for(int j=0;j<w;j++){
                if(i==0 || j==0 || i==w || j==h)
                    continue;
                else{
                    int id = i*w+h;
                    if(t[(id-w)/w][(id-w)%w] == 1)
                        matrix[id][id-w] = 1;
                    if(t[(id+w)/w][(id+w)/w] == 1)
                        matrix[id][id+w] = 1;
                    if(t[(id-1)/w][(id-1)/w] == 1)
                        matrix[id][id-1] = 1;
                    if(t[(id+1)/w][(id+1)/w] == 1)
                        matrix[id][id+1] = 1;
                }
            }
        }
        int count = 1;
        queue<int> Q;
        int came[w*h];
        for(int i=0;i<w*h;i++){
            came[i] = 0;
        }
        Q.push(start);
        came[start] = 1;
        while(Q.size()!=0){
            int cur = Q.front();
            for(int i=0;i<w*h;i++){
                if(matrix[cur][i]==1 && came[i] == 0){
                    Q.push(i);
                    came[i] = 1;
                    count++;
                }
            }
            Q.pop();
        }
        cout << count << endl;
    }
}

C++: #if 0
?????????????????????????????????
#endif

#include <iostream>
#include <queue>
#include <string.h>
#include <utility>
using namespace std;

int w,h;

const int dx[]={1,0,-1,0}, dy[]={0,-1,0,1}; //??????????§??????¨
char P[100][100]; //??§?¨?????????????????????¨???

bool valid(int x,int y){ //??????????????????
	return (x>=0)&&(x<w)&&(y>=0)&&(y<h)&&(P[x][y]!='#');
}

void bfs(int x,int y){ //???????????¢?´¢
	int tot=1; //?????£????????????(?????????????????????)
	queue<pair<int,int> > q;
	pair<int,int> p;
	p = make_pair(x,y); //pair??????????????¨??????????????????
	q.push(p);
	while(!q.empty()){
		pair<int,int> cur=q.front(); //?????¨??°?????????????????????
		q.pop();
		for(int i=0;i<4;++i){
			if(valid(cur.first+dx[i],cur.second+dy[i])){
				q.push(make_pair(cur.first+dx[i],cur.second+dy[i]));
				tot++;
				P[cur.first+dx[i]][cur.second+dy[i]]='#'; //???????????£?????´???????°???????
			}
		}
		P[cur.first][cur.second]='#';
	}
	cout << tot <<endl;
}

int main(){
	int x1,y1;
	while((cin>>w>>h)&&(w!=0)){
		for(int j=0;j<h;++j){
			for(int i=0;i<w;++i){
				cin>>P[i][j];
				if(P[i][j]=='@')
					x1=i; y1=j; 
			}
		}
		bfs(x1,y1); //??????????????°????????£??\????????¢?´¢????§?
	}
}

C++: #include <functional>
#include <algorithm>
#include <iostream>
#include <numeric>
#include <iomanip>
#include <utility>
#include <cstdlib>
#include <sstream>
#include <bitset>
#include <vector>
#include <cstdio>
#include <ctime>
#include <queue>
#include <deque>
#include <cmath>
#include <stack>
#include <list>
#include <map>
#include <set>

using namespace std;

typedef vector<int> vi;
typedef pair<int,int> pii;
typedef long long ll;

#define dump(x)  cerr << #x << " = " << (x) << endl
#define rep(i,n) for(int i=0;i<(n);i++)
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define all(a)  (a).begin(),(a).end()
#define pb push_back
#define sz size()

const double EPS = 1e-10;
const int INF = 100000000;

int x,y;
char fie[100][100]={};
char visited[100][100]={};
int c;


void dfs(int sx,int sy){
    if(sx<0 || sy<0 || sx>=x || sy>=y)return;
    if(visited[sy][sx])return;
    if(fie[sy][sx]!='.' && fie[sy][sx]!='@')return;
    c++;
    visited[sy][sx]=true;
    
    int d[5]={-1,0,1,0,-1};
    rep(i,4){
        dfs(sx+d[i],sy+d[i+1]);
    }
}

int main(){
    
    
    while(cin>>x>>y){
        c=0;
        rep(i,100)
        rep(j,100)
        visited[i][j]=false;
        
        int sx=-1,sy=-1;
        if(x==0 && y==0)break;
        
        rep(i,y){
            rep(j,x){
                cin>>fie[i][j];
                if(fie[i][j]=='@'){
                    sx=j,sy=i;
                }
            }
        }
        dfs(sx,sy);
        cout<<c<<endl;
    }
    
    return 0;
}