Go: // AOJ 1160: How Many Islands? http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=1160

package main

import (
	"bufio"
	"container/list"
	"fmt"
	"os"
	"strconv"
)

var SEA = 0
var LAND = 1

func nextInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

func discoverIslands(M, V [][]int, H, W int) int {
	// 島を探す
	queue := list.New()
	islands := 0
	for i := 1; i <= H; i++ {
		for j := 1; j <= W; j++ {
			// 訪問済みの土地ならスキップ
			if V[i][j] == 1 {
				continue
			}

			// 訪問中の土地が海なら訪問済みにしてスキップ
			if M[i][j] == SEA {
				V[i][j] = 1
				continue
			}

			// 未訪問の陸地が見つかったので
			// 島の数を1つ増やし、この陸地から辿れる陸地を訪問していく
			islands++
			queue.PushBack([]int{i, j})

			for queue.Len() > 0 {
				cur := queue.Remove(queue.Front()).([]int)
				h, w := cur[0], cur[1]
				if V[h][w] == 1 {
					continue
				}
				V[h][w] = 1

				// 全方向に未訪問の陸地がないか探索
				for v := -1; v <= 1; v++ {
					for l := -1; l <= 1; l++ {
						dh := h + v
						dw := w + l
						if M[dh][dw] == LAND && V[dh][dw] == 0 {
							queue.PushBack([]int{dh, dw})
						}
					}
				}
				/*
					if M[h-1][w] == LAND {
						queue.PushBack([]int{h - 1, w})
					}
					if M[h-1][w+1] == LAND {
						queue.PushBack([]int{h - 1, w + 1})
					}
					if M[h][w+1] == LAND {
						queue.PushBack([]int{h, w + 1})
					}
					if M[h+1][w+1] == LAND {
						queue.PushBack([]int{h + 1, w + 1})
					}
					if M[h+1][w] == LAND {
						queue.PushBack([]int{h + 1, w})
					}
					if M[h+1][w-1] == LAND {
						queue.PushBack([]int{h + 1, w - 1})
					}
					if M[h][w-1] == LAND {
						queue.PushBack([]int{h, w - 1})
					}
					if M[h-1][w-1] == LAND {
						queue.PushBack([]int{h - 1, w - 1})
					}
				*/
			}
		}
	}
	return islands
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	for {
		W, H := nextInt(sc), nextInt(sc)

		if W == 0 && H == 0 {
			break
		}
		// Initialize map and visted list
		M := make([][]int, H+2)
		V := make([][]int, H+2)
		for i := 0; i < H+2; i++ {
			M[i] = make([]int, W+2)
			V[i] = make([]int, W+2)
		}
		for i := 1; i <= H; i++ {
			for j := 1; j <= W; j++ {
				M[i][j] = nextInt(sc)
			}
		}

		islands := discoverIslands(M, V, H, W)

		fmt.Println(islands)
	}
}

C++: #include<iostream>

using namespace std;

int h, w, map[51][51];

const int vx[] = {1,0,-1,0}, vy[] = {0,1,0,-1};

void island(int _w, int _h) {
	map[_w][_h] = 2;
	for (int i = 0;i < 4;i++) {
		if (_w + vy[i] >= 1 && _w + vy[i] <= h&&_h + vx[i] >= 1 && _h + vx[i] <= w&&map[_w+vy[i]][_h+vx[i]] == 1) {
			island(_w + vy[i], _h + vx[i]);
		}
	}
}

int main() {
	while (cin >> w >> h, w + h) {
		for (int i = 1;i <= h;i++) {
			for (int j = 1;j <= w;j++) {
				cin >> map[i][j];
			}
		}
		int count = 0;
		for (int i = 1;i <= h;i++) {
			for (int j = 1;j <= w;j++) {
				if (map[i][j] == 1) {
					count++, island(i, j);
				}
			}
		}
		cout << count << endl;
		for (int i = 1;i <= 50;i++)for (int j = 1;j <= 50;j++)map[i][j] = -1;
	}
	return 0;
}

C++: #include<iostream>
#include<math.h>
#include<stdlib.h>
#include<string>
#include<limits.h>
#include<vector>
using namespace std;
typedef long long ll;
bool search(int i, int j, vector<vector<int>>& c, vector<vector<bool>> &gone) {
	if (gone[i][j])return false;
	if (c[i][j] == 0)return false;
	gone[i][j] = true;
	for (int I = -1; I < 2; I++) {
		for (int J = -1; J < 2; J++) {
			if(i+I>=0&&j+J>=0&&i+I<c.size()&&j+J<c[0].size())
			search(i + I, j + J, c, gone);
		}
	}
	return true;
}
int main() {
	int w, h;
	while (true) {
		cin >> w >> h;
		if (w == 0 && h == 0) {
			return 0;
		}
		vector<vector<int>> c(h, vector<int>(w, 0));
		for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++) {
				cin >> c[i][j];
				//cout << c[i][j] << " ";
			}
			//cout << endl;
		}
		vector<vector<bool>> gone(h, vector<bool>(w, false));
		int ans=0;
		for (int i = 0; i < h; i++) {
			for (int j = 0; j < w; j++) {
				if (search(i, j, c, gone)) {
					ans++;
				}
			}
		}
		cout << ans << endl;
	}
}