Go: package main

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

var (
	n     int
	G     [100000][]int
	color [100000]*int
)

func dfs(r int, c int) {
	S := Stack{}
	S.Push(r)
	color[r] = &c
	for !S.IsEmpty() {
		u := S.Pop()
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == nil {
				color[v] = &c
				S.Push(v)
			}
		}
	}
}

func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = nil
	}
	for u := 0; u < n; u++ {
		if color[u] == nil {
			id++
			dfs(u, id)
		}
	}
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Scan()
	n, _ = strconv.Atoi(sc.Text())
	sc.Scan()
	r, _ := strconv.Atoi(sc.Text())

	for i := 0; i < r; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}
	assignColor()
	sc.Scan()
	qNum, _ := strconv.Atoi(sc.Text())
	for i := 0; i < qNum; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

// Stack is Stack
type Stack struct {
	stack []int
}

// Push new value
func (stack *Stack) Push(val int) {
	stack.stack = append(stack.stack, val)
}

// Pop new value
func (stack *Stack) Pop() int {
	val := stack.stack[len(stack.stack)-1]
	stack.stack = stack.stack[0 : len(stack.stack)-1]
	return val
}

// IsEmpty return true when stack is empty
func (stack *Stack) IsEmpty() bool {
	return len(stack.stack) == 0
}

C++: 
import java.util.*;


public class Main{ 

	public static void main(String args[]){
		Scanner scan = new Scanner(System.in);
		Graph graph = new Graph(scan.nextInt());
		int relationNum = scan.nextInt();
		for(int i=0; i<relationNum; i++)
			graph.setRelation(scan.nextInt(), scan.nextInt());
		int queryNum = scan.nextInt();
		for(int i=0; i<queryNum; i++)
			if(graph.bfs(scan.nextInt(), scan.nextInt())==-1)
				System.out.println("no");
			else
				System.out.println("yes");
		//graph.bfs(16);

	}

}
class Graph{
	int verNum;
	ArrayList<Node> vertices;
	public Graph(int n){
		vertices = new ArrayList<Node>();
		this.verNum = n;
		for(int i=0; i<verNum;i++)
			vertices.add(new Node(i));
	}
	public void setRelation(int a, int b){
		vertices.get(a).addNext(vertices.get(b));
	}
	public Graph(int[][] matrix){
		vertices = new ArrayList<Node>();
		for(int i=0; i<matrix.length;i++)
			vertices.add(new Node(i+1));
		for(int i=0; i<matrix.length;i++)
			for(int j=0; j<matrix.length; j++)
				if(matrix[i][j]!=0)
					vertices.get(i).addNext(vertices.get(j));
	}
	void walk(){
		int time = 0;
		for(int i=0; i<vertices.size();i++){
			time = vertices.get(i).walk(time);
		}
	}
	void nearest(){	
		//for(int i=0; i<vertices.size();i++)
			//System.out.println((i+1) + " " + bfs(i+1));
	}
	void clearHistory(){
		for(int i=0; i<vertices.size();i++)
					vertices.get(i).disSteped();	
	}
	void print(){

		for(int i=0; i<vertices.size();i++)
			vertices.get(i).result();
	}

	int bfs(int start, int target){
		ArrayDeque<Node> queue = new ArrayDeque<Node>();
		clearHistory();
		queue.addFirst(vertices.get(start));
		int dist = 0;
		int childCount = 1;
		int nextChildrenCount=0;
		while(!queue.isEmpty()){
			Node temp = queue.removeLast();
			if(temp.id==target)
				return dist;
			childCount--;

			for(Node n : temp.nextNode){
				if(!n.steped){
					n.steped = true;
					nextChildrenCount++;
					queue.addFirst(n);
				}
			}
			if(childCount==0){
				dist++;
				childCount = nextChildrenCount;
				nextChildrenCount=0;
			}
			//System.out.println("queue size : " + queue.size());
		}
		return -1;

	}
}

class Node{
	int id;
	int startTime;
	int endTime;
	boolean steped = false;
	ArrayList<Boolean> stepedNext = new ArrayList<Boolean>(); 
	ArrayList<Node> nextNode = new ArrayList<Node>();
	public Node(int id){
		this.id = id;
	}
	public void addNext(Node n){
		nextNode.add(n);
		stepedNext.add(false);
	}
	public void disSteped(){
		this.steped = false;
	}
	
	public int walk(int time){
		if(this.steped)
			return time;
		time++;//
		this.startTime = time;
		this.steped = true;
		int end = time;
		for(int i=0; i<stepedNext.size(); i++){
			time = nextNode.get(i).walk(time);
		}
		time++;//
		this.endTime = time;
		return endTime;
	}
	boolean remainNext(){
		return stepedNext.contains(false);
	}
	void result(){
		System.out.println(this.id + " " + startTime + " " + endTime);
	}
}
class AdjacencyMatrices{
	int pointNum;
	int[][] matrix;
	public AdjacencyMatrices(int n){
		pointNum = n;
		matrix = new int[n][];
		for(int i=0; i<n; i++)
			matrix[i] = new int[n];
	}
	public void readList(Scanner scan){
		for(int i=0; i<pointNum; i++){
			int index = scan.nextInt()-1;
			int dim = scan.nextInt();
			for(int j=0; j< dim; j++)
				matrix[index][scan.nextInt()-1] = 1;
		}
	}
	public int[][] getMatrix(){
		return matrix;
	}
	public void printMatrix(){
		StringBuilder temp = new StringBuilder();
		for(int i=0; i<pointNum; i++){
			for(int j=0; j<pointNum; j++){
				temp.append(matrix[i][j]);
				if(j!=pointNum-1)
					temp.append(" ");
			}
			temp.append("\n");
		}
		System.out.print(new String(temp));
	}

}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
static const int MAX=100000;
static const int NIL=-1;

int n;
vector<int> g[MAX];
int color[MAX];

void dfs(int r,int c){
  stack<int> s;
  s.push(r);
  color[r]=c;
  while(!s.empty()){
    int u=s.top();
    s.pop();
    for(int i=0;i<g[u].size();i++){
      int v=g[u][i];
      if(color[v]==NIL){
	color[v]=c;
	s.push(v);
      }
    }
  }
}

void assignColor(){
  int id=1;
  for(int i=0;i<n;i++) color[i]=NIL;
  for(int u=0;u<n;u++){
    if(color[v]==NIL) dfs(u,id++);
  }
}

int main(){
  int s,t,m,q;

  cin>>n>>m;

  for(int i=0;i<m;i++){
    cin>>s>>t;
    g[s].push_back(t);
    g[t].push_back(s);
  }

  assignColor();

  cin>>q;

  for(int i=0;i<q;i++){
     cin>>s>>t;
     if(color[s]==color[t]){
       cout<<"yes"<<endl;
     }else{
       cout<<"no"<<endl;
     }
  }
  return 0;
}

C++: #include <iostream>
#include <vector>
#include <queue>

using namespace std;

int WHITE = 0;
int GRAY = 1;
int BLACK = 2;

#define MAX 100000

int color[MAX];
vector<int> G[MAX];
int reach[MAX];

void find_route(int s) {
  queue<int> S;

  S.push(s);
  color[s] = GRAY;

  reach[s] = s;

  while(!S.empty()){
    int v = S.front(); S.pop();

    for (int i = 0; i < (int)G[v].size(); i++) {
      int u = G[v][i];

      if(color[u] == WHITE) {
        color[u] = GRAY;
        reach[u] = s;
        S.push(u);
      }
    }
  }
}

int main() {
  for(int i = 0; i < MAX; i++) color[i] = WHITE;
  for (int i = 0; i < MAX; i++) reach[i] = -1;

  int n, m;
  cin >> n >> m;

  for (int i = 0; i < m; i++) {
    int u, v;
    cin >> u >> v;

    G[u].push_back(v);
    G[v].push_back(u);
  }

  for(int i = 0; i < MAX; i++) {
    if(color[i] != GRAY) {
      find_route(i);
    }
  }

  int q;
  cin >> q;
  for (int i = 0; i < q; i++) {
    int s, t;
    cin >> s >> t;

    if(reach[s] != -1 && reach[s] == reach[t]) {
      cout << "yes";
    } else {
      cout << "no";
    }
    cout << endl;
  }

  return 0;
}