C :

#include<stdio.h>

int W, H;
int count;
int vis[30][30];
char str[30][30];

struct Point{
    int x, y;
}Start;

int dx[]={-1,0,1,0}, dy[]={0,1,0,-1};

void Scan_Point();//输入函数
void DFS(struct Point p);//执行函数

int main()
{
    while(scanf("%d%d",&H,&W)){
        if(W==0 && H==0) break;
        count=1;
        Scan_Point();
        DFS(Start);
        printf("%d\n",count);
    }
    return 0;
}

void Scan_Point(){
    int i, j;
    getchar();
    for(i=0; i<W; i++){
        for(j=0; j<H; j++){
            scanf("%c",&str[i][j]);
            vis[i][j]=1;
            if(str[i][j]=='@'){
                Start.x=i;
                Start.y=j;
            }
        }
        getchar();
    }
}

void DFS(struct Point p){
    int a, b;
    int i, j;
    struct Point temp;
    for(i=0; i<4; i++){
        a=p.x+dx[i]; b=p.y+dy[i];
        temp.x=a; temp.y=b;
        if(a>=0 && a<W && b>=0 && b<H && str[a][b]=='.' && vis[a][b]){
            count++;
            vis[a][b]=0;
            DFS(temp);
        }
    }
    return ;
}

C++ :

#include<iostream>
#include<cstring>
#include<queue>
using namespace std;

struct N
{
	int x,y;
}start,head,tail;

char g[20][20];
int w,h,sum,v[20][20],f[][2]={{-1,0},{0,-1},{1,0},{0,1}};

int bfs()
{
	sum=0;
	memset(v,0,sizeof(v));
	v[start.x][start.y]=1;
	queue<struct N> q;
	q.push(start);
	while(!q.empty())
	{
		sum++;
		head=q.front();
		q.pop();
		for(int i=0;i<4;i++)
		{
			tail.x=head.x+f[i][0];
			tail.y=head.y+f[i][1];
			if(!v[tail.x][tail.y]&&tail.x>=0&&tail.x<h&&tail.y>=0&&tail.y<w&&g[tail.x][tail.y]=='.')
			{
				q.push(tail);
				v[tail.x][tail.y]=1;
			}
		}
	}
	return sum;
}

int main()
{
	int i,j;
	while(cin>>w>>h,w||h)
	{
		for(i=0;i<h;i++)
			for(j=0;j<w;j++)
			{
				cin>>g[i][j];
				if(g[i][j]=='@')
				{
					start.x=i;
					start.y=j;
				}
			}
		cout<<bfs()<<endl;
	}
	return 0;
}

Java :

import java.util.Scanner;


public class Main {
	static int m,n;
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		while(in.hasNextInt()){
			n = in.nextInt();
			m = in.nextInt();
			if(n==0&&m==0)
				break;
			String[] s = new String[m];
			char[][] maze = new char[m][n];
			int[][] idx = new int[m][n];
			for(int i=0;i<m;i++){
				s[i] = in.next();
				maze[i] = s[i].toCharArray();
			}
			for(int i=0;i<m;i++){
				for(int j=0;j<n;j++){
					if(idx[i][j]==0&&maze[i][j]=='@')
						dfs(i,j,idx,maze,1);
				}
			}
			int cnt=0;
			for(int i=0;i<m;i++)
				for(int j=0;j<n;j++){
					if(idx[i][j]>0)
						cnt++;
				}
			System.out.println(cnt);
		}
	}
	public static void dfs(int r,int c,int[][]idx,char[][] maze,int id){
		if(r<0||r>=m||c<0||c>=n)
			return;
		if(idx[r][c]>0||maze[r][c]=='#')
			return;
		idx[r][c] = id;
		
		dfs(r+1,c,idx,maze,id);
		dfs(r-1,c,idx,maze,id);
		dfs(r,c+1,idx,maze,id);
		dfs(r,c-1,idx,maze,id);
	}
}