DFS

#include<cstring>
using namespace std;
typedef pair<int, int> PII;
char s[30][30];
bool t[30][30];
int n, m;
int dx[4] = {1, -1, 0, 0}, dy[4] = {0, 0, 1, -1};
int dfs(PII st) {
	t[st.first][st.second] = true;
	int ans = 1;
	for (int i = 0; i < 4; i ++) {
		int x = dx[i] + st.first, y = dy[i] + st.second;
		if (x >= 1 && x <= m && y >= 1 && y <= n && s[x][y] == '.' && !t[x][y]) {
			t[x][y] = true;
			PII c = {x, y};
			ans += dfs(c);
		}
	}
	return ans;
}
int main() {

	while (cin >> n >> m) {
		if (!n && !m) break;
		PII st;
		for (int i = 1; i <= m; i ++) {
			for (int j = 1; j <= n; j ++) {
				cin >> s[i][j];
				if (s[i][j] == '@') {
					st = {i, j};
				}
			}
		}
		memset(t, 0, sizeof t);
		int ans = dfs(st);
		cout << ans << endl;
	}
	return 0;
}

BFS

#include<cstring>
#include<queue>
using namespace std;
#define x first
#define y second
typedef pair<int, int> PII;
char s[30][30];
bool t[30][30];
int n, m;
int dx[4] = {1, -1, 0, 0}, dy[4] = {0, 0, 1, -1};
int bfs(PII st) {
	t[st.x][st.y] = true;
	queue<PII>q;
	int ans = 1;
	q.push(st);
	while(q.size())
	{
	PII f = q.front();
	q.pop();
	for (int i = 0; i < 4; i ++) {
		int x = dx[i] + f.x, y = dy[i] + f.y;
		if(x >= 1 && x <= m && y >= 1 && y <= n && s[x][y] == '.' && !t[x][y]) {
			t[x][y] = true;
			PII c = {x, y};
			q.push(c);
			ans ++;
		}
	}
	}
	return ans;
}
int main() {

	while(cin >> n >> m){
	if(!n && !m) break;
	PII st;
	for (int i = 1; i <= m; i ++) {
		for (int j = 1; j <= n; j ++) {
			cin >> s[i][j];
			if (s[i][j] == '@') {
				st = {i, j};
			}
		}
	}
	memset(t,0,sizeof t);
	int ans = bfs(st);
	cout << ans << endl;
	}
	return 0;
}