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>
using namespace std;

int main()
{
	int w, h;
	while (true) {
		cin >> w >> h;
		if (w == 0 && h == 0) {
			break;
		}
		unsigned next = 1U;
		char** room = new char*[h];
		unsigned** group = new unsigned*[h];
		int x, y;
		for (int i = 0; i < h; i++) {
			room[i] = new char[w];
			group[i] = new unsigned[w];
			for (int j = 0; j < w; j++) {
				cin >> room[i][j];
				if (room[i][j] == '@') {
					x = j;
					y = i;
				}
				group[i][j] = 0U;
			}
		}

		for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++) {
				if (room[i][j] != '#') {
					for (int a = i - 1; a <= i + 1; a++) {
						for (int b = j - 1; b <= j + 1; b++) {
							if (a < 0 || b < 0 || a >= h || b >= w) {
								continue;
							}
							if ((a == i && b != j) || (a != i && b == j)) {
								group[i][j] |= group[a][b];
							}
							if (group[i][j] == 0U) {
								group[i][j] |= next;
								next <<= 1;
							}
						}
					}
				}
			}
		}
		for (int i = h - 1; i >= 0; i--) {
			for (int j = w - 1; j >=0; j--) {
				if (room[i][j] != '#') {
					for (int a = i - 1; a <= i + 1; a++) {
						for (int b = j - 1; b <= j + 1; b++) {
							if (a < 0 || b < 0 || a >= h || b >= w) {
								continue;
							}
							if ((a == i && b != j) || (a != i && b == j)) {
								group[i][j] |= group[a][b];
								if (group[i][j] == 0U) {
									group[i][j] |= next;
									next <<= 1;
								}
							}
						}
					}
				}
			}
		}
		for (int j = 0; j < w; j++) {
			for (int i = 0; i < h; i++) {
				if (room[i][j] != '#') {
					for (int a = i - 1; a <= i + 1; a++) {
						for (int b = j - 1; b <= j + 1; b++) {
							if (a < 0 || b < 0 || a >= h || b >= w) {
								continue;
							}
							if ((a == i && b != j) || (a != i && b == j)) {
								group[i][j] |= group[a][b];
								if (group[i][j] == 0U) {
									group[i][j] |= next;
									next <<= 1;
								}
							}
						}
					}
				}
			}
		}
		for (int j = w - 1; j >= 0; j--) {
			for (int i = h - 1; i >= 0; i--) {
				if (room[i][j] != '#') {
					for (int a = i - 1; a <= i + 1; a++) {
						for (int b = j - 1; b <= j + 1; b++) {
							if (a < 0 || b < 0 || a >= h || b >= w) {
								continue;
							}
							if ((a == i && b != j) || (a != i && b == j)) {
								group[i][j] |= group[a][b];
								if (group[i][j] == 0U) {
									group[i][j] |= next;
									next <<= 1;
								}
							}
						}
					}
				}
			}
		}
		int count = 0;
		for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++) {
				if (group[i][j] & group[y][x]) {
					count++;
				}
			}
		}

		cout << count << '\n';

		for (int i = 0; i < h; i++) {
			delete[] room[i];
			delete[] group[i];
		}
		delete[] room;
		delete[] group;
	}

	return 0;
}

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

int W, H;
char b[20][20];
int ans;
int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};

void dfs(int x, int y) {
	ans++;
	b[y][x] = '#';
	for (int i = 0; i < 4; i++) {
		int nx = x + dx[i], ny = y + dy[i];
		if (0 <= nx && nx < W && 0 <= ny && ny < H && b[ny][nx] == '.') {
			dfs(nx, ny);
		}
	}
}

int main() {
	while (cin >> W >> H , W) {
		for (int y = 0; y < H; y++) {
			for (int x = 0; x < W; x++) {
				cin >> b[y][x];
			}
		}

		for (int y = 0; y < H; y++) {
			for (int x = 0; x < W; x++) {
				if (b[y][x] == '@') {
					ans = 0;
					dfs(x, y);
				}
			}
		}

		cout << ans << endl;
	}
}