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++: // Ref : https://book.mynavi.jp/ec/products/detail/id=35408

#include <iostream>
#include <vector>
#include <stack>

using namespace std;
static const int NMAX = 100000;
static const int NIL = -1;

int n, group[NMAX];
vector<int> G[NMAX];

void depthFirstSearch(int ix, int id) {
	int y;
	stack<int> S;
	S.push(ix);
	while (!S.empty()) {
		ix = S.top(); S.pop();
		for (unsigned int j = 0; j < G[ix].size(); j++) {
			y = G[ix][j];
			if (group[y] == NIL) {
				group[y] = id;
				S.push(y);
			}
		}
	}
}

void classifyID() {
	int id = 0;
	for (int i = 0; i < n; i++) {
		if (group[i] == NIL) {
			depthFirstSearch(i, id);
			id++;
		}
	}
}

int main(void) {
	int m, x, y;

	cin >> n >> m;
	for (int i = 0; i < n; i++) group[i] = NIL; // initialize group list
	for (int i = 0; i < m; i++) { // create graph in linked list representation
		cin >> x >> y;
		G[x].push_back(y);
		G[y].push_back(x);
	}

	classifyID();

	cin >> n;

	for (int i = 0; i < n; i++) {
		cin >> x >> y;
		if ((group[x] != NIL) && (group[y] != NIL) && (group[x] == group[y]))
			cout << "yes";
		else
			cout << "no";
		cout << 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;
	if(d[a]!=d[b]){
		int k=d[b];
		for(int h=0;h<n;h++){
			if(d[h]==k){
				d[h]=d[a];
			}
		}
		
		
	}
}
cin>>q;
for(int y=0;y<q;y++){
	int a,b;
	cin>>a>>b;
	if(d[a]==d[b]){
		cout<<"yes"<<endl;
	}
	else{
		cout<<"no"<<endl;
	}
}
	return 0;
}

C++: #include <iostream>
#include <vector>
#define N 100000
#define white 0

int color[N], n, S[N];
std::vector<int> c[N];



void tansaku_2(int a, int b) {
    int i, t, co, u;
    S[0] = a;
    t = 0;
    co = 1;
    while (1) {
        u = S[t];
        for (i = 0; i < c[u].size(); ++i) {
            if (color[c[u][i]] == white){
                color[c[u][i]] = b;
                S[co++] = c[u][i];
            }
        }
        S[t++] = 0;
        if (t == co) break;
    }
}

void tansaku() {
    int i, d;
    d = 1;
    
    for (i = 0; i < n; ++i) {
        if (color[i] == white) {
            color[i] = d;
            tansaku_2(i , d++);
        }
    }
}

int main() {
    int m, q, i, a, b;
    
    scanf("%d %d", &n, &m);
    for (i = 0; i < n; ++i) {
        color[i] = white;
    }
    for (i = 0; i < m; ++i) {
        scanf("%d %d", &a, &b);
        c[a].push_back(b);
        c[b].push_back(a);
    }
    tansaku();
    
    scanf("%d", &q);
    for (i = 0; i < q; ++i) {
        scanf("%d %d", &a, &b);
        if (color[a] == color[b]) {
            printf("yes\n");
        }
        else{
            printf("no\n");
        }
    }
    return 0;
}