Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

func newGraph(nNodes int) *Graph {
	g := Graph{}
	g.nodes = make([]*GraphNode, nNodes)
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode] = &GraphNode{}
		g.nodes[iNode].key = GraphNodeKey(iNode)
	}
	return &g
}

var infty = 1000000000

type GraphNodeKey int

// GraphNode is a node for undirected graph
type GraphNode struct {
	key       GraphNodeKey
	adjacents []*GraphNode
	visited   bool
	d, f      int
	parent    *GraphNode
	cc        int
}

func (g *Graph) setAdjacent(l, r GraphNodeKey) {
	g.nodes[l].adjacents = append(g.nodes[l].adjacents, g.nodes[r])
}

// Graph is a undirected graph
type Graph struct {
	nodes []*GraphNode
}

func (g *Graph) initialize() {
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode].visited = false
		g.nodes[iNode].d = infty
		g.nodes[iNode].f = infty
		g.nodes[iNode].parent = nil
		g.nodes[iNode].cc = -1 // 22.3-12
	}
}

type QueueEntry struct {
	node *GraphNode
	next *QueueEntry
}

type Queue struct {
	head, tail *QueueEntry
}

func (q *Queue) enqueue(node *GraphNode) {
	entry := QueueEntry{}
	entry.node = node

	if q.tail == nil {
		q.head = &entry
		q.tail = &entry
		return
	}

	q.tail.next = &entry
	q.tail = q.tail.next
}

func (q *Queue) dequeue() *QueueEntry {
	if q.head == nil {
		return nil
	}
	poped := q.head
	q.head = q.head.next
	if q.head == nil {
		q.tail = nil
	}
	return poped
}

func (q *Queue) isEmpty() bool {
	return q.head == nil
}

var time = 0

func fillDistancesByDepthFirstSearch(g *Graph) {
	g.initialize()
	time = 0
	cc := 0

	for _, u := range g.nodes {
		if !u.visited {
			dfsVisit(g, u, cc)
			cc++
		}
	}
}

func dfsVisit(g *Graph, u *GraphNode, cc int) {
	time++
	u.d = time
	u.cc = cc

	u.visited = true
	for _, v := range u.adjacents {
		if !v.visited {
			v.parent = u
			dfsVisit(g, v, cc)
		}
	}
	time++
	u.f = time
}

func main() {
	scanner.Split(bufio.ScanWords)

	nUsers := nextInt()
	nEdges := nextInt()
	graph := newGraph(nUsers)
	for iEdge := 0; iEdge < nEdges; iEdge++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())
		graph.setAdjacent(l, r)
		graph.setAdjacent(r, l)
	}

	fillDistancesByDepthFirstSearch(graph)

	nQueries := nextInt()
	for iQuery := 0; iQuery < nQueries; iQuery++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())

		// fmt.Println(graph.nodes[l].d, graph.nodes[r].d, graph.nodes[r].f, graph.nodes[l].f)
		if graph.nodes[l].cc == graph.nodes[r].cc {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

C++: #include <stdio.h>
#include <iostream>
#include <queue>
#include <list>
using namespace std;

queue<int> que;

class Node
{
private:
	//int next_num;
	//int *next_node_list;
	list<int> next_node_list;
public:
	Node();
	void AddNextNode(int id);
	bool Search(int st, int ed);
	bool check; //!
	//bool *check;
	//bool *link;
};

Node::Node()
{
	//next_num = 0;
	check = false;
	/*check = new bool[n];
	for (int i = 0; i < n; i++) {
		check[i] = false;
	}*/
	/*link = new bool[n];
	for (int i = 0; i < n; i++) {
		link[i] = false;
	}*/
}

void Node::AddNextNode(int id)
{
	next_node_list.push_back(id);
	//next_node_list[next_num] = id;
	//next_num++;
}

Node *Node_list;

bool Node::Search(int st, int ed)
{
	//if (link[ed]) return true;

	/*for (int k = 0; k < next_num; k++) {
		Node_list[st].link[next_node_list[k]] = true;
		Node_list[next_node_list[k]].link[st] = true;
	}*/

	/*for (int i = 0; i < next_num; i++) {
		if (next_node_list[i] == ed) return true;
	}*/
	list<int>::iterator itr;
	for(itr = next_node_list.begin(); itr != next_node_list.end(); itr++){
		if (*itr == ed) return true;
	}
	
	/*for (int j = 0; j < next_num; j++) {
		//if (Node_list[next_node_list[j]].check[ed] == 0) {
		if (Node_list[next_node_list[j]].check == 0) { //!
		//	Node_list[next_node_list[j]].check[ed] = 1;
			Node_list[next_node_list[j]].check = 1; //!
			que.push(next_node_list[j]);
		}
	}*/
	for(itr = next_node_list.begin(); itr != next_node_list.end(); itr++){
		if (Node_list[*itr].check == 0) {
			Node_list[*itr].check = 1;
			que.push(*itr);
		}
	}
	
	return false;
}

int main(void)
{
	//input
	int n;
	cin >> n;
	Node_list = new Node[n]();
	int m;
	cin >> m;
	for (int i = 0; i < m; i++) {
		int s, t;
		cin >> s >> t;
		Node_list[s].AddNextNode(t);
		Node_list[t].AddNextNode(s);
	}
	
	//output
	int q;
	cin >> q;
	for (int i = 0; i < q; i++) {
		int s, t;
		cin >> s >> t;
		//Node_list[s].check[t] = true;
		Node_list[s].check = true; //!
		bool ret = Node_list[s].Search(s, t);
		while (!ret && !que.empty()) {
			ret = Node_list[que.front()].Search(s, t);
			que.pop();
		};

		while (!que.empty()) {
			que.pop();
		}
		for (int j = 0; j < n; j++) {
			//Node_list[j].check[t] = false;
			Node_list[j].check = false; //!
		}

		if (ret) {
			cout << "yes" << "\n";
		}
		else {
			cout << "no" << "\n";
		}
	}
	
	return 0;
}

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[N];

void dfs(int r, int c) {
  stack<int> S;
  S.push(s);
  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[u] == NIL) {
      dfs(u, id++);
    }
  }
}

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

  cin >> n >> m;

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

  assignColor();

  int q;
  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 <cstdio>
#include <queue>
#include <vector>

typedef struct{
	std::vector<int> neighbors;
	int cluster;
} node;

void dfs(node* nodes, int id, int cluster){
	for (int i=0; i<nodes[id].neighbors.size(); i++){
		if (nodes[nodes[id].neighbors[i]].cluster == -1){
			nodes[nodes[id].neighbors[i]].cluster = cluster;
			dfs(nodes, nodes[id].neighbors[i], cluster);
		}
	}
}

int main(){
	int n, d, num_relation, n_query, s, t, cluster;
	node *nodes;

	scanf("%d %d", &n, &num_relation);
	nodes = new node[n];
	for (int i=0; i<n;i++){
		nodes[i].cluster = -1;
	}
	for(int i=0;i<num_relation;i++){
		scanf("%d %d", &s, &t);
		nodes[s].neighbors.push_back(t);
		nodes[t].neighbors.push_back(s);
	}
	cluster = -1;
	for (int i=0;i<n;i++){
		cluster ++;
		if (nodes[i].cluster == -1) dfs(nodes, i, cluster);
	}
	scanf("%d", &n_query);
	for(int i=0;i<n_query;i++){
		scanf("%d %d", &s, &t);
		if (nodes[s].cluster == nodes[t].cluster) printf("yes\n");
		else printf("no\n");

	}

	delete []nodes;
	return 0;
}