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<cstring>
#include<algorithm>
#include<cstdio>
#include<stack>
using namespace std;
const int MAXN = 100000 + 7;
const int NIL = -1;

vector<int> G[MAXN];
int status[MAXN];
int N;

void dfs( int  r, int c )
{
    stack<int> S;
    S.push(r);
    status[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 ( status[v] == NIL ) {
                status[v] = c;
                S.push(v);
            }
        }
    }
}

void set_status()
{
    int id = 1;
    memset( status, -1, sizeof(status) );
    for ( int u = 0; u < N; u++ ) {
        if ( status[u] == NIL )
            dfs( u, id++ );
    }
}

int main()
{
    int 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);
    }

    set_status();

    cin>>q;
    for ( int i = 0; i < q; i++ ) {
        cin>>s>>t;
        if ( status[s] == status[t] ) cout<<"yes"<<endl;
        else cout<<"no"<<endl;
    }
    return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cassert>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define rep(i,n) FOR(i,0,n)
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define vint vector<int>
#define vdouble vector<double>
#define vstring vector<string>
using namespace std;

#include<map>
#include<set>
#include<queue>

typedef long long ll;
typedef unsigned long long ull;

const int MAX_N = 1000000;

struct UnionFind
{
	// par[i]????????????i????±?????????¨??????????????????i == par[i]?????¨???????????????i?????¨?????????????????§??????
	// sizes[i]???????????????i?????¨?????????????????????????????°???i?????????????????§????????´???????????????????????¨??????
	vector<int> par;
	vector<int> sizes;

	UnionFind(int n) : par(n), sizes(n, 1) {
		rep(i, n) par[i] = i;
	}

	int find(int x) {
		if (x == par[x]) return x;
		return par[x] = find(par[x]); // ????????????????????????????????°???????????????????????¢???
	}

	void unite(int x, int y) {
		x = find(x);
		y = find(y);

		if (x == y) return;

		// x?????¨???y?????¨????????§???????????????????????????
		if (sizes[x] < sizes[y]) swap(x, y);

		par[y] = x; // ??????????????????????????°??????
		sizes[x] += sizes[y];
		sizes[y] = 0;  // sizes[y]????????????????????¨???????????§0?????\????????????????????????
	}

	bool same(int x, int y) {
		return find(x) == find(y);
	}

	int size(int x) {
		return sizes[find(x)];
	}
};

int N, M, Q;

int main() {

	cin >> N >> M;
	UnionFind uf(N);
	rep(i, M){
		int f1, f2; cin >> f1 >> f2;
		uf.unite(f1, f2);
	}
	cin >> Q;
	rep(i, Q)
	{
		int f1, f2; cin >> f1 >> f2;
		cout << (uf.same(f1, f2) ? "yes" : "no") << endl;
	}

}

C++: #include <iostream>
#include <queue>
using namespace std;
struct Node{
    vector<int> fri;
    bool flag;
};
queue<Node> refresh(queue<Node> que,Node node[],int n){
    while(!que.empty())
        que.pop();
    
    for(int i=0; i<n; i++)
        node[i].flag=false;

    return que;
}

int main(){
    int n,m,s,t;
    Node node[100000];
    cin >> n >> m;

    for(int i=0; i<m; i++){
        cin >> s >> t;

        node[s].fri.push_back(t);
        node[t].fri.push_back(s);
    }

    queue<Node> que;
    refresh(que,node,n);

    int q;
    cin >> q;

    bool answer[10000];
    for(int i=0; i<q; i++){
        answer[i]=false;
        cin >> s >> t;

        node[s].flag=true;
        que.push(node[s]);

        while(!que.empty() && !answer[i]){
         Node fro = que.front();

         for(int j=0; j<fro.fri.size(); j++){
            int x = fro.fri[j];
  
            if(!node[x].flag){
                node[x].flag=true;
                que.push(node[x]);

		if(x==t){
		  answer[i]=true;
		  break;
		}
            }
         }

          que.pop();
        }

        que=refresh(que,node,n);
    }

    for(int i=0; i<q; i++){
        if(answer[i])
            cout << "yes\n";
        else
            cout << "no\n";
    }
}