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 <iostream>
#include <cmath>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
using namespace std;
const int MAXN = 100100 ;
inline int read()
{
	int f = 1, x = 0; char c = getchar();
	while (c < '0' || c > '9') {if (c == '-') f = -1; c = getchar();}
	while (c >= '0' && c <= '9') {x = (x << 3) + (x << 1) + c - '0'; c = getchar();}
	return f * x;
}
int f[MAXN], n, m, q;
int getfa(int x)
{
	if (f[x] == x) return f[x];
	return f[x] = getfa(f[x]);
}
int main()
{
	n = read(); m = read();
	for (int i = 0; i < n; ++i) f[i] = i;
	for (int i = 1, u, v; i <= m; ++i)
	{
		u = read(); v = read();
		int fa1 = getfa(u);
		int fa2 = getfa(v);
		if (fa1 != fa2)
			f[fa1] = fa2;
	}
	q = read();
	for (int i = 1; i <= q; ++i)
	{
		int u, v;
		u = read(); v = read();
		int fa1 = getfa(u), fa2 = getfa(v);
		if (fa1 == fa2) cout << "yes" << endl;
		else cout << "no" << endl;
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
int n, m;
vector< list<int> > v;
vector<bool> used;

int main(void){
  ios::sync_with_stdio(false);
  cin.tie(0);

  cin >> n >> m;
  v = vector< list<int> >(n, list<int>(0));
  used = vector<bool>(n, false);
  for(int i = 0; i < m; i++){
    int a, b; cin >> a >> b;
    v[a].push_back(b);
    v[b].push_back(a);
  }
  int q; cin >> q;
  for(int i = 0; i < q; i++){
    used = vector<bool>(n, false);
    int a, b; cin >> a >> b;
    bool flg = false;
    queue<int> que;
    que.push(a);
    while(!que.empty()){
      int q = que.front(); que.pop();
      for(list<int>::iterator it = v[q].begin(); it != v[q].end(); it++){
        if(*it == b){
          flg = true;
          break;
        }
        if(used[*it]) continue;
        used[*it] = true;
        que.push(*it);
      }
      if(flg) break;
    }
    if(flg) cout << "yes" << endl;
    else cout << "no" << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <map>
#include <queue>
using namespace std;
int main(){
  int n,m,t1,t2,c[100000]={}; map <int,bool> g[100000];
  cin>>n>>m;
  for(int i=0;i<m;i++){
    cin>>t1>>t2;g[t1][t2]=1;g[t2][t1]=1;
  }
  int l;cin>>l;
  for(int i=0;i<l;i++){
    queue <int> q;
    bool f[100000]={},find=false;
    cin>>t1>>t2;
    if(c[t1]){
      if(c[t1]==c[t2]) cout<<"yes"<<endl;
      else cout<<"no"<<endl;
      continue;
    }
    q.push(t1);f[t1]=true;c[t1]=i+1;
    for(;!q.empty();){
      for(int j=0;j<n;j++) if(g[q.front()][j]&&!f[j]){
          if(j==t2) find=true;
          f[j]=true;c[t2]=i+1;
          q.push(j);
	}
      q.pop();
      if(find) break;
    }
    if(find) cout<<"yes"<<endl;
    else cout<<"no"<<endl;
  }
  return 0;
}

C++: #include <iostream>
#include <vector>
using namespace std;
#define MAX 100000
#define NIL -1

vector<int> G[MAX];
int c, top, S[MAX], color[MAX];

void dfs_init(int n){
  top = 0;
  for(int i=0; i<n; i++){
    color[i] = NIL;
  }
}

void dfs(int s){
  int v;
  color[s] = c;
  S[++top] = s;
  while(top > 0){
    s = S[top];
    top--;
    for(int i = 0; i<G[s].size(); i++){
      v = G[s][i];
      if(color[v] == NIL){
        S[++top] = v;
        color[v] = c;
      }
    }
  }
}

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

  dfs_init(n);
  for(int i=0; i<n; i++){
    if(color[i] == NIL){
      dfs(i);
      c++;
    }
  }

  c = 0;
  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<stack>
using namespace std;
static const int Max = 100000
static const int NIL = 100000
int i, j, v, num, color[Max];
vector<int> list[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(i=0; i<list[u].size(); i++){
     v = list[u][i];
     if(color[v] == NIL){
       color[v] = c;
       S.push(v);
     }
   }
 }
}
  
void assigncolor(){
 int id = 1;
 for(i=0; i<num; i++){
   color[i] = NIL;
 }
 for(j=0; j<num; j++){
   if(color[j] == NIL)
     dfs(i, id++);
 }
}
  
int main(){
 int a, b, trial, start, goal, kaisuu;
 cin >> num >> kaisuu;
  
 for(i=0; i<kaisuu; i++){
   cin >> a >> b;
   list[a].push_back(b);
   list[b].push_back(a);
 }
 
 assigncolor();
 
 cin >> trial;
 
 for(i=1; i<=trial; i++){
   cin >> start >> goal;
   if(color[start] == color[goal]){  
     cout << "yes" << endl;
   } else{
     cout << "no" << endl;
   }
 }
  
 return 0;
}