POJ 1979 Red and Black

#include<iostream>
#include<cstdio>
#include<queue>
#include<algorithm>
#include<cstring>
using namespace std;
#define MAXN 21
struct node
{
    int x;
    int y;
};
int n,m,g[MAXN][MAXN];
bool vis[MAXN][MAXN];
int x[4]={1,-1,0,0};
int y[4]={0,0,1,-1};
int bfs(int sx,int sy)
{
    int ans = 0;
    node temp;
    temp.x = sx;
    temp.y = sy;
    vis[sx][sy] = true;
    queue<node> q;
    q.push(temp);
    while(!q.empty())
    {
        temp = q.front();
        q.pop();
        //cout<<temp.x<<' '<<temp.y<<endl;
        ans++;
        for(int i=0;i<4;i++)
        {
            int tx = temp.x + x[i];
            int ty = temp.y + y[i];
            if((tx>=0&&ty>=0&&tx<m&&ty<n)&&!vis[tx][ty]&&g[tx][ty]=='.')
            {
                vis[tx][ty] = true;
                node nn;
                nn.x = tx;
                nn.y = ty;
                q.push(nn);
            }
        }
    }
    return ans;
}
int main()
{
    while(scanf("%d%d",&n,&m))
    {
        getchar();
        if(n+m==0) break;
        int sx,sy;
        memset(g,0,sizeof(g));
        memset(vis,false,sizeof(vis));
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                scanf("%c",&g[i][j]);
                if(g[i][j]=='@')
                {
                    sx = i;
                    sy = j;
                }
            }
            getchar();
        }
        cout<<bfs(sx,sy)<<endl;
    }
    return 0;
}