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 <cstdint>
#include <vector>

using namespace std;

#define GRAPH_SIZE 100000

enum state_t {
  WHITE,
  GRAY,
  BLACK,
};

struct vertex_t {
  uint32_t color;
  vector<uint32_t> connections;
};

static vertex_t graph[GRAPH_SIZE];
static state_t state[GRAPH_SIZE];

static void colorize(uint32_t index, uint32_t color)
{
  if (state[index] == WHITE) {
    state[index] = GRAY;
    graph[index].color = color;
    for (uint32_t i = 0; i < graph[index].connections.size(); i++) {
      colorize(graph[index].connections[i], color);
    }
    state[index] = BLACK;
  }
}

void check_connection(size_t num)
{
  for (uint32_t i = 0; i < num; i++) {
    state[i] = WHITE;
  }

  uint32_t color = 1;
  for (uint32_t i = 0; i < num; i++) {
    colorize(i, color);
    color++;
  }
}

#include <iostream>

int32_t main()
{
  uint32_t n, m;
  cin >> n >> m;

  for (uint32_t i = 0; i < m; i++) {
    uint32_t index, to;
    cin >> index >> to;
    graph[index].connections.push_back(to);
    graph[to].connections.push_back(index);
  }

  check_connection(n);

  uint32_t qs;
  cin >> qs;

  for (uint32_t i = 0; i < qs; i++) {
    uint32_t from, to;
    cin >> from >> to;

    if (graph[from].color == graph[to].color) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }

  return 0;
}

C++: #include <iostream>
using namespace std;
  
int main() {
int d[100100];
int m,n,q;
cin>>n>>m;
for(int i=0;i<n;i++){
    d[i]=i;
}
for(int l=0;l<m;l++){
    int a,b;
    cin>>a>>b;
    int j ,h;
    j=a,h=b;
while(d[j]!=j && d[h]!=h){
    j=d[j];
    h=d[h];
}
if(d[j]==j){
	while(d[h]!=h){
		h=d[h];
	}
    d[j]=h;
    d[a]=h;
d[b]=h;
}
else{
	while(d[j]!=j){
		j=d[j];
	}
  d[h]=j;
    d[b]=j;
d[a]=h;
}
}
cin>>q;
for(int y=0;y<q;y++){
    int a,b;
    cin>>a>>b;
        int j ,h;
    j=a,h=b;
while(d[j]!=j || d[h]!=h){
    j=d[j];
    h=d[h];
}
    if(j==h){
        cout<<"yes"<<endl;
    }
    else{
        cout<<"no"<<endl;
    }
}
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

vector<int> g[100000];
int c[100000],n;


void dfs(int r,int a){
  stack<int> s;
  s.push(r);
  c[r]=a;
  while(!s.empty()){
    int u=s.top();
    s.pop();
    for(int i=0;i<g[u].size();i++){
      int v=g[u][i];
      if(c[v]==-1){
	c[v]=a;
	s.push(v);
      }
    }
  }
}

void color(){
  int id=1;
  for(int i=0;i<n;i++) c[i]=-1;
  for(int i=0;i<n;i++){
    if(c[i]==-1) dfs(i,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);
  }
  color();
  cin>>q;
  for(int i=0;i<q;i++){
    cin>>s>>t;
    if(c[s]==c[t]) cout<<"yes"<<endl;
    else cout<<"No"<<endl;
  }
  return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>

class queue{
    int head;
    int tail;
    int size;
    int *q;
public:
    queue(int n){
        head=0;
        tail=0;
        size=n;
        q = (int *)malloc(sizeof(int)*size);
    }
    void push(int n){
        if(tail-head>=size){
            return;
        }
//        printf("%d in.\n",n);
        q[tail%size]=n;
        tail++;
    }
    int pop(){
        if(tail<=head){
            return -1;
        }
        head++;
        return q[(head-1)%size];
    }
};

bool isFriend(int s, int t,int n,char **f,int *kakunin,int c){
    bool hoge;
    int tmp;
    queue ob(n);
    ob.push(s);
    kakunin[s]=c;
    for(int i=0;i<n;i++){
        hoge = true;
        while(true){
            tmp = ob.pop();
            if(tmp==-1)return false;
            for(int j=0;j<n;j++){
                if(f[tmp][j]&&(kakunin[j]<c)){
                    ob.push(j);
                    kakunin[j] = c;
                    f[s][j] = 1;
                    hoge = false;
                    if(j==t)return true;
                }
            }
        }
        if(hoge)return false;
    }
    return false;
}

int main(){
    int i,j,k,s,t,q,n,m;

    scanf("%d %d",&n,&m);

    char **f = (char **)malloc(sizeof(char *)*n);
    int *kakunin = (int *)malloc(sizeof(int)*n);
    memset(kakunin,0,sizeof(int)*n);

    for(i=0;i<n;i++){
        f[i] = (char *)malloc(sizeof(char)*n);
        memset(f[i],0,sizeof(char)*n);
    }

    for(i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        f[s][t] = 1;
        f[t][s] = 1;
    }

    scanf("%d",&q);
    for(i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        if(isFriend(s,t,n,f,kakunin,i+1))printf("yes\n");
        else printf("no\n");
    }
    return 0;
}