Go: package main

import (
	"bufio"
	"os"
	"strconv"
	"fmt"
	"strings"
	"sort"
)

var scanner= bufio.NewScanner(os.Stdin)

func main() {
	for scanner.Scan() {
		n, _ := strconv.Atoi(scanner.Text())
		if n == 0 {
			break
		}
		mp := make([]string, n)
		for i := range mp {
			scanner.Scan()
			mp[i] = "0" + scanner.Text() + "0"
		}
		tmp := make([]string, n+2)
		for i := range tmp {
			tmp[i] = "0"
		}
		mp = append([]string{strings.Join(tmp, "")}, mp...)
		mp = append(mp, strings.Join(tmp, ""))
		score := make([][][]int, n+2)
		for i := range score {
			score[i] = make([][]int, n+2)
			for j := range score[i] {
				score[i][j] = make([]int, 4)
			}
		}
		max_score := 0
		for i := 1; i < n+1; i++ {
			for j := 1; j < n+1; j++ {
				tmps := mp[i]
				if string(tmps[j]) == "1" {
					score[i][j][0] = score[i - 1][j][0] + 1
					score[i][j][1] = score[i][j - 1][1] + 1
					score[i][j][2] = score[i - 1][j - 1][2] + 1
					score[i][j][3] = score[i - 1][j + 1][3] + 1
					max_score = max(max_score, score[i][j][0], score[i][j][1], score[i][j][2], score[i][j][3])
				}
			}
		}
		fmt.Println(max_score)
	}
}

func max(a, b, c, d, e int) int {
	buf := []int{a, b, c, d, e}
	sort.Ints(buf)
	return buf[len(buf)-1]
}

C++: #include <bits/stdc++.h>
using namespace std ;

#define pb(n) push_back(n)
#define fi first
#define se second
#define all(r) (r).begin(),(r).end()
#define gsort(st,en) sort((st),(en),greater<int>())
#define vmax(ary) *max_element(all(ary))
#define vmin(ary) *min_element(all(ary))
#define debug(x) cout<<#x<<": "<<x<<endl
#define fcout(n) cout<<fixed<<setprecision((n))
#define scout(n) cout<<setw(n)
#define vary(type,name,size,init) vector< type> name(size,init)

#define rep(i,n) for(int i = 0; i < (int)(n);++i)
#define REP(i,a,b) for(int i = (a);i < (int)(b);++i)
#define repi(it,array) for(auto it = array.begin(),end = array.end(); it != end;++it)
#define repa(n,array) for(auto &n :(array))

using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using dict = map<string,int>;
using pii = pair<int,int> ;

constexpr int imax = ((1<<30)-1)*2+1 ;
constexpr int inf = 100000000;
constexpr double PI = acos(-1.0) ;
double eps = 1e-10 ;
const int dy[] = {-1,0,1,0};
const int dx[] = {0,-1,0,1};

inline bool value(int x,int y,int w,int h){
  return (x >= 0 && x < w && y >= 0 && y < h);
}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n;
  while(cin>>n && n){
    vector<vector<char>> vc(n,vector<char>(n,' '));
    rep(i,n){
      rep(j,n){
        cin >>vc[j][i];
        vc[j][i] -= '0';
      }
    }
    auto tmp = vc;
    char ma = 0;
    rep(i,n){
      rep(j,n){
        if( j > 0 && tmp[j][i]){
          tmp[j][i] += tmp[j-1][i];
        }
        ma = max(ma,tmp[j][i]);
      }
    }
    tmp = vc;
    rep(j,n){
      rep(i,n){
        if( i > 0 && tmp[j][i]){
          tmp[j][i] += tmp[j][i-1];
        }
        ma = max(ma,tmp[j][i]);
      }
    }
    //??????->??????
    tmp = vc;
    rep(i,n){
      rep(j,n){
        if( j < n-1 && i > 0&& tmp[j][i]){
          tmp[j][i] += tmp[j+1][i-1];
        }
        ma = max(ma,tmp[j][i]);
      }
    }
    //??????->??????
    tmp = vc;
    rep(i,n){
      rep(j,n){
        if( j > 0 && i > 0 && tmp[j][i]){
          tmp[j][i] += tmp[j-1][i-1];
        }
        ma = max(ma,tmp[j][i]);
      }
    }
    cout << (int)ma << endl;
  }
  return 0;
}

C++: #include<bits/stdc++.h>
using namespace std ;

int n,cnt ;
char table[260][260] ;
int dx[] = {-1,-1,0,1,1,1,0,-1} ;
int dy[] = {0,-1,-1,-1,0,1,1,1} ;

int f( int y , int x ){
	int cnt = 0 , c[4] = {} ;
	for( int k=0 ; k<8 ; k++ ){
		int nx = x+dx[k] , ny = y+dy[k] ;
		while( table[ny][nx] == '1' ){
			c[k%4]++ ;
			nx += dx[k] ;
			ny += dy[k] ;
		}
	}
	for( int k=0 ; k<4 ; k++ ) cnt = max( cnt , c[k]+1 ) ;
	return cnt ;
}

main(){
	while( cin >> n , n ){
		for( int i=0 ; i<=n+1 ; i++ ){
			for( int j=0 ; j<=n+1 ; j++ ){
				if( !i || !j || i==n+1 || j==n+1 ) table[i][j] = '0' ;
				else cin >> table[i][j] ;
			}
		}
		
		int ans = 0 ;
		for( int i=1 ; i<=n ; i++ ){
			for( int j=1 ; j<=n ; j++ ){
				if( table[i][j] == '1' ){
					f(i,j) ;
					ans = max( ans , f(i,j) ) ;
				}
			}
		}
		
		cout << ans << endl ;
	}
}

C++: #define _USE_MATH_DEFINES
#include <iostream>
#include <sstream>
#include <cmath>
#include <algorithm>
#include <queue>
#include <stack>
#include <limits>
#include <map>
#include <string>
#include <cstring>
#include <set>
#include <deque>
#include <bitset>

using namespace std;

typedef long long ll;
typedef pair<int,int> P;

static const double eps = 10e-6;

int mat[255][255];

int diagLLUR(int n,int** mat){
	int res = 0;
	for(int y=0;y<n;y++){
		int isok = 1;
		for(int x=0,dy=y;x<n,dy>=0;x++,dy--){
			if(mat[dy][x] == 0) isok = 0;
		}
		res = max((y+1)*isok,res);
	}

	for(int x=0;x<n;x++){
		int isok = 1;
		for(int dx=x,y=n-1;dx<n,y>=0;dx++,y--){
			if(mat[y][dx] == 0) isok = 0;
		}
		res = max((n-x)*isok,res);
	}

	return res;
}

int diagULLR(int n,int** mat){
	int res = 0;
	for(int x=n-1;x>=0;x--){
		int isok = 1;
		for(int dx=x,y=0;dx<n,y<n;dx++,y++){
			if(mat[y][dx] == 0) isok = 0;
		}
		res = max((n-x)*isok,res);
	}

	for(int y=0;y<n;y++){
		int isok = 1;
		for(int x=0,dy=y;x<n,dy<n;x++,dy++){
			if(mat[dy][x] == 0) isok = 0;
		}
		res = max((n-y)*isok,res);
	}

	return res;
}

int vert(int n,int** mat){
	int res = 0;
	for(int x=0;x<n;x++){
		int isok = 1;
		for(int y=0;y<n;y++){
			if(mat[y][x] == 0) isok = 0;
		}

		res = max(n*isok,res);
	}

	return res;
}

int hori(int n,int** mat){
	int res = 0;
	for(int y=0;y<n;y++){
		int isok = 1;
		for(int x=0;x<n;x++){
			if(mat[y][x] == 0) isok = 0;
		}

		res = max(n*isok,res);
	}

	return res;
}

int main(){

	int n;	

	while(~scanf("%d",&n)){
		if(n==0) break;

		int** mat = new int*[n];
		for(int i=0;i<n;i++) mat[i] = new int[n]();

		for(int y=0;y<n;y++){
			char buf[128];
			scanf("%s",buf);
			for(int x=0;x<n;x++){
				mat[y][x] = buf[x]-'0';
			}
		}
		printf("%d\n",max(max(diagLLUR(n,mat),hori(n,mat)),max(diagULLR(n,mat),vert(n,mat))));

		for(int i=0;i<n;i++) delete[] mat[i];
		delete[] mat;
	}
}

C++: #include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define repb(i, a, b) for(int i = a; i >= b; i--)
#define all(a) a.begin(), a.end()
#define int long long
#define fi first
#define se second
using namespace std;


signed main(){
    int n;
    while(cin >> n, n){
        int MAX = 0;
        vector<string> d(256);
        rep(i, 0, n) cin >> d[i];
        rep(i ,0, n){
            rep(j, 0, n){
                if(d[i][j] == '0') break;
                if(j == n - 1) MAX = n;
            }
        }
        rep(i, 0, n){
            rep(j, 0, n){
                if(d[j][i] == '0') break;
                if(j == n - 1) MAX = n;
            }
        }
        rep(i, 0, n){
            int l = n - i;
            rep(j, 0, l){
                if(d[i + j][j] == '0') break;
                if(j == l - 1) MAX = max(MAX, l);
            }
        }
        rep(i, 0, n){
            int l = n - i;
            rep(j, 0, l){
                if(d[j][i + j] == '0') break;
                if(j == l - 1) MAX = max(MAX, l);
            }
        }
        rep(i, 0, n){
            int l = i + 1;
            rep(j, 0, l){
                if(d[i - j][j] == '0') break;
                if(j == l - 1) MAX = max(MAX, l);
            }
        }
        rep(i, 0, n){
            int l = n - i;
            rep(j, 0, l){
                if(d[i + j][n - 1 - j] == '0') break;
                if(j == l - 1) MAX = max(MAX, l);
            }
        }
        cout << MAX << endl;
    }
}