like this:

#include<bits/stdc++.h>
using namespace std;
int n,m,a[505][505],ans;
void bfs(){
	for(int i=2;i<=n+1;i++){
		for(int j=2;j<=m+1;j++){
			if((a[i][j-1]==4 || a[i-1][j]==4 || a[i+1][j]==4 || a[i][j+1]==4) && a[i][j]!=1){
 				a[i][j]=4;
			}
		}
	}
}
//4 5
//00000
//00*00
//0*0*0
//00*00
int main(){
	cin>>n>>m;
    char e;
    for(int i=2;i<=n+1;i++){
        for(int j=2;j<=m+1;j++){
            cin>>e;
            if(e=='*')a[i][j]=1;
            else a[i][j]=0;
        }
    }
    if(a[2][2]==0){a[2][2]=4;}
    if(a[2][m+1]==0){a[2][m+1]=4;}
    if(a[n+1][2]==0){a[n+1][2]=4;}
    if(a[n+1][m+1]==0){a[n+1][m+1]=4;}
    bfs();
    for(int i=2;i<=n+1;i++){
    	for(int j=2;j<=m+1;j++){
    		cout<<a[i][j]<<' ';
    		if(a[i][j]==0){
    			ans++;
    		}
    	}
    	cout<<endl;
    }
    cout<<ans;
	return 0;
}

but it WA,why?pleas healp,healp!