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 <cstdlib>
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
//_____
#define pb push_back
#define mkp make_pair
#define rep(i,n) for(int i=0; i<(n); ++i)
#define reps(i,f,n) for(int i=(f); i<=(n); ++i)
#define outl(x) cout << (x) << '\n'
#define FAST() cin.tie(0), ios::sync_with_stdio(false)
//_______

vector <int> G[100005];
int group[100005];
int color = 1;

void dfs(int u)
{
   group[u] = color;

   rep(i, G[u].size())
      if( group[ G[u][i] ] == 0 )dfs( G[u][i] );
}

signed main()
{
   FAST();
   int N, M;
   cin >> N >> M;

   rep(i, M){
      int a,b;
      cin >> a >> b;
      G[a].pb(b);
      G[b].pb(a);
   }

   rep(i, N){
      if(group[i] == 0 )dfs(i);
      ++color;
   }

   int Q;
   cin >> Q;
   while(Q--){
      int a,b;
      cin >> a >> b;
      outl( group[a] == group[b] ? "yes" : "no" );
   }
}

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[u] == 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 <stdio.h>
#include <algorithm>
#include <queue>

using namespace std;

struct Info{
	Info(){s = t = -1;}
	Info(int tmp_s,int tmp_t){
		s = tmp_s;
		t = tmp_t;
	}
	int s;
	int t;
};

class Relation{
public:
	Relation(int tmp_n,int tmp_m){
		n = tmp_n;
		m = tmp_m;
		global = new Info[m];
		each = new int*[n];
		each_index = new int[n];
		num_of_each = new int[n];
		for(int i=0;i<n;i++){
			each_index[i] = 0;
			num_of_each[i] = 0;
		}
		global_index = 0;
	}

	void push(int s,int t){
		global[global_index++] = Info(s,t);
		num_of_each[s]++;
		num_of_each[t]++;
	}

	void allocate(){
		for(int i=0;i<n;i++){
			if(num_of_each[i] > 0){
				each[i] = new int[num_of_each[i]];
			}
		}
		Info tmp;
		for(int i=0;i<m;i++){
			tmp = global[i];
			each[tmp.s][each_index[tmp.s]++] = tmp.t;
			each[tmp.t][each_index[tmp.t]++] = tmp.s;
		}
	}

	bool canAccsess(int s,int t){
		queue<int> Q;
		Q.push(s);
		int node,went[n];
		for(int i=0;i<n;i++)went[i]=0;
		while(!Q.empty()){
			node = Q.front();
			went[node] = 1;
			Q.pop();
			for(int i=0;i<num_of_each[node];i++){
				if(each[node][i] == t) return true;
				else if(went[each[node][i]] == 0){
					Q.push(each[node][i]);
				}
			}
		}
		return false;
	}

private:
	Info* global;
	int** each;
	int* each_index;
	int* num_of_each;
	int global_index,n,m;
};

int main(){
	int n,m,s,t,q;
	scanf("%d %d",&n,&m);

	Relation relation(n,m);
	for(int i=0;i<m;i++){
		scanf("%d %d",&s,&t);
		relation.push(s,t);
	}
	relation.allocate();
	scanf("%d",&q);
	for(int i=0;i<q;i++){
		scanf("%d %d",&s,&t);
		if(relation.canAccsess(s,t)){
			printf("yes\n");
		}else{
			printf("no\n");
		}
	}
    return 0;
}