水过。注意边界不能超出。

#include 
      
       using namespace std;int n, m, sx, sy, dir[4][2] = {
     0, -1, 0, 1, 1, 0, -1, 0}, count;char diagram[23][23];void get_diagram(void) {    for (int i = 0; i < n; i++) {        for (int j = 0; j < m; j++) {            cin >> diagram[i][j];            if (diagram[i][j] == '@') {                sx = i;                sy = j;            }        }    }}void dfs(int x, int y) {    count++;    diagram[x][y] = '#';    for (int i = 0; i < 4; i++) {        if (x + dir[i][0] >=0 && x + dir[i][0] < n && y + dir[i][1] >= 0 && y + dir[i][1] < m && diagram[x + dir[i][0]][y + dir[i][1]] != '#') {            dfs(x + dir[i][0], y + dir[i][1]);        }    }    return;}int main(void) {    while (cin >> m >> n, n*n + m*m) {        get_diagram();        count = 0;        dfs(sx, sy);        cout << count << endl;    }    return 0;}