Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N, M := sc.nextInt(), sc.nextInt()
	G := make([][]int, N)
	for i := 0; i < M; i++ {
		s, t := sc.nextInt(), sc.nextInt()
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}
	group := make([]int, N)
	for i := 0; i < N; i++ {
		group[i] = -1
	}
	var dfs func(cur int)
	dfs = func(cur int) {
		for i := 0; i < len(G[cur]); i++ {
			next := G[cur][i]
			if group[next] == -1 {
				group[next] = group[cur]
				dfs(next)
			}
		}
	}
	num := 0
	for i := 0; i < N; i++ {
		if group[i] == -1 {
			group[i] = num
			dfs(i)
			num++
		}
	}

	Q := sc.nextInt()
	for i := 0; i < Q; i++ {
		s, t := sc.nextInt(), sc.nextInt()
		if group[s] == group[t] {
			fmt.Fprintln(wtr, "yes")
		} else {
			fmt.Fprintln(wtr, "no")
		}
	}
	wtr.Flush()
}

C++: #include <algorithm>
#include <iostream>
#include <string>
#include <vector>

class TUser
{
	std::vector<TUser*> FAccessible;
	bool FVisited;

public:
	TUser();
	void AddFriend(TUser* Friend);
	bool IsAccesible(TUser* Target);
};

TUser::TUser()
:FVisited(false)
{
}

void TUser::AddFriend(TUser* Friend)
{
	if(std::find(FAccessible.begin(), FAccessible.end(), Friend) != FAccessible.end()) return;
	FAccessible.push_back(Friend);
}

bool TUser::IsAccesible(TUser* Target)
{
	if(FVisited) return false;
	FVisited = true;
	if(std::find(FAccessible.begin(), FAccessible.end(), Target) != FAccessible.end()) return true;
	for(unsigned int i = 0; i < FAccessible.size(); ++i){
		if(FAccessible[i]->IsAccesible(Target)) return true;
	}
	return false;
}

class TSns
{
	std::vector<TUser> FUsers;
public:
	TSns(int UserCount);
	
	void AddLink(int UserA, int UserB);
	std::string IsAccesible(int UserA, int UserB);
};

TSns::TSns(int UserCount)
: FUsers(UserCount)
{
}

void TSns::AddLink(int UserA, int UserB)
{
	FUsers[UserA].AddFriend(&FUsers[UserB]);
	FUsers[UserB].AddFriend(&FUsers[UserA]);
}

std::string TSns::IsAccesible(int UserA, int UserB)
{
	if(FUsers[UserA].IsAccesible(&FUsers[UserB])) return "yes";
	return "no";
}

int main()
{
	int UserCount;
	std::cin >> UserCount;
	TSns Sns(UserCount);
	
	int LinkCount;
	std::cin >> LinkCount;
	for(int i = 0; i < LinkCount; ++i){
		int UserA, UserB;
		std::cin >> UserA >> UserB;
		Sns.AddLink(UserA, UserB);
	}
	
	int QuestionCount;
	std::cin >> QuestionCount;
	for(int i = 0; i < QuestionCount; ++i){
		int UserA, UserB;
		std::cin >> UserA >> UserB;
		std::cout << Sns.IsAccesible(UserA, UserB) << std::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[a]=j;
d[b]=j;
}

}
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;

const int maxn=1e5+5;
const int NIL=-1;

int n,color[maxn];
vector<int>g[maxn];

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;
}
/*
10 9
0 1
0 2
3 4
5 7
5 6
6 7
6 8
7 8
8 9
3
0 1
5 9
1 3
*/

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

    for(int i=0; i<n; i++)
        node[i].flag=false;
}

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

            if(!node[x].flag){
                node[x].flag=true;
                que.push(node[x]);
            }
         }

          que.pop();
        }

        refresh(que,node,n);
    }

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