Language: C++

#include <bits/stdc++.h>
using namespace std;
typedef unsigned int uint;
typedef long long int lint;
typedef unsigned long long int ulint;

//#define DEBUG

#ifdef DEBUG
#	define dump(i) cout << "[*] " #i " : " << i << endl;
#	define debug(i) i
void print(char map[20][20], int w, int h) {
	for (int i = 0; i < h; ++i) {
		for (int j = 0; j < w; ++j) {
			cout << static_cast<int>(map[i][j]);
		}
		cout << endl;
	}
}
void print(int* arr, int size) {
	for (int i = 0; i < size; ++i) {
		cout << arr[i] << endl;
	}
}
#else
#	define dump(i)
#	define debug(i)
# define print(i, j, k)
# define print(j, k)
#endif
#define rep(i, MAX) for (int i = 0; i < (MAX); ++i)

struct UnionFind
{
	vector<int> par;

	UnionFind(int n): par(n) {
		for (int i = 0; i < n; ++i) {
			par[i] = i;
		}
	}

	int find(int x) {
		if (x == par[x]) return x;
		return par[x] = find(par[x]);
	}

	bool same(int x, int y) {
		return find(x) == find(y);
	}

	void unite(int x, int y) {
		x = find(x);
		y = find(y);
		if (x == y) return;
		par[y] = x;
	}
};

inline void solve() {
	int w, h;
	constexpr int MAX = 20;
	char tile[MAX][MAX];
	dump(MAX);

	while (true) {
		pair<int, int> at;
		cin >> w >> h;
		if (!w && !h) return;
		int table[MAX] = {};
		UnionFind uf = UnionFind(200);

		const int asdf = MAX * MAX;
		dump(asdf);
		rep(i, h) {
			rep(j, w) {
				cin >> tile[i][j];
				if (tile[i][j] == '@') {
					at.first = i;
					at.second = j;
					tile[i][j] = '.';
				}
			}
		}
		int csi = 1;
		if (tile[0][0] == '.') {
			tile[0][0] = csi++;
		} else {
			tile[0][0] = 0;
		}
		table[tile[0][0]]++;
		for (int i = 1; i < w; ++i) {
			if (tile[0][i] == '.') {
				tile[0][i] = tile[0][i-1] != 0 ? tile[0][i-1] : csi++;
			} else {
				tile[0][i] = 0;
			}
			table[tile[0][i]]++;
		}
		rep(i, h) {
			if (i == 0) continue;
			rep(j, w) {
				if (j == 0) {
					if (tile[i][j] == '.') {
						tile[i][j] = tile[i-1][j] != 0 ? tile[i-1][j] : csi++;
					} else {
						tile[i][j] = 0;
					}
				} else {
					if (tile[i][j] == '.') {
						int tmp = tile[i-1][j];
						if (tmp == 0) {
							tmp = tile[i][j-1];
						} else if (tile[i][j-1] != 0) {
							uf.unite(tmp, tile[i][j-1]);
							if (tmp > tile[i][j-1]) {
								tmp = tile[i][j-1];
							}
						}
						tile[i][j] = tmp != 0 ? tmp : csi++;
					} else {
						tile[i][j] = 0;
					}
				}
				table[tile[i][j]]++;
			}
		}
		int ans = 0;
		int iv = tile[at.first][at.second];
		rep(i, csi) {
			if (uf.same(iv, i)) {
				ans += table[i];
			}
		}
		dump("tile");
		print(tile, w, h);
		dump("table");
		print(table, csi);
		dump("ans");
		cout << ans << endl;
	}
}

int main() {
	//*
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	// */
#ifdef DEBUG
	const auto start = chrono::high_resolution_clock::now();
#endif
	solve();
#ifdef DEBUG
	const auto stop = chrono::high_resolution_clock::now();
	cerr << "[*] time: " << chrono::duration_cast<chrono::milliseconds>(stop-start).count()
		<< " [ms]" << endl;
#endif
	return 0;
}



Compiler output:
a.cc:29:10: warning: "print" redefined
   29 | # define print(j, k)
      |          ^~~~~
a.cc:28:10: note: this is the location of the previous definition
   28 | # define print(i, j, k)
      |          ^~~~~
a.cc:136:33: error: macro "print" passed 3 arguments, but takes just 2
  136 |                 print(tile, w, h);
      |                                 ^
a.cc:29:10: note: macro "print" defined here
   29 | # define print(j, k)
      |          ^~~~~
a.cc: In function 'void solve()':
a.cc:136:17: error: 'print' was not declared in this scope
  136 |                 print(tile, w, h);
      |                 ^~~~~