总体写的还算简洁明了

#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdlib>
using namespace std;
const int N = 30;
char arr[N][N];
int vis[N][N];
int ans = 0;
int dx[] = {-1,0,1,0},dy[] = {0,1,0,-1};
void dfs(int x,int y,int n,int m) {
    if (x > m || x < 1 || y > n || y < 1 || vis[x][y] || arr[x][y] == '#')  return;
    ans++;
    vis[x][y] = 1;
    for (int i = 0;i < 4;i++) {
        dfs(x + dx[i],y + dy[i],n,m);
    }
    return;
}
int main() {
    int n,m;
    cin >> n >> m;
    while (n != 0 && m != 0) {
        ans = 0;
        memset(vis,0,sizeof(int) * N * N);
        int start_x,start_y;
        for (int i = 1;i <= m;i++) {
            for (int j = 1;j <= n;j++) {
                cin >> arr[i][j];
                if (arr[i][j] == '@') {
                    start_x = i;
                    start_y = j;
                }
            }
        }
        dfs(start_x,start_y,n,m);
        cout << ans << endl;
        cin >> n >> m;
    }
    return 0;
}