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 <iostream>
#include <vector>
using namespace std;

vector< int > connections;

void addConnection(int a, int b) {
  if (connections[a] == a && connections[b] == b)
    a < b ? connections[b] = a : connections[a] = b;
  else if (connections[a] == a)
    addConnection(a, connections[b]);
  else if (connections[b] == b)
    addConnection(connections[a], b);
  else
    addConnection(connections[a], connections[b]);
}

bool checkConnection(int a, int b) {
  if (connections[a] == a && connections[b] == b) {
    if (a == b)
      return true;
    else
      return false;
  } else if (connections[a] == a) {
    return checkConnection(a, connections[b]);
  } else if (connections[b] == b) {
    return checkConnection(connections[a], b);
  } else
    return checkConnection(connections[a], connections[b]);
}

int main(int argc, char **argv) {
  ios_base::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  connections = vector< int > (n, -1);
  for (int i = 0; i < n; i++)
    connections[i] = i;
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    addConnection(a, b);
  }
  int q;
  cin >> q;
  // for (int i = 0; i < n; i++)
  //   cout << connections[i] << ' ';
  // cout << endl;
  for (int i = 0; i < q; i++) {
    int a, b;
    cin >> a >> b;
    // cout << a << ' ' << b << endl;
    if (checkConnection(a, b))
      cout << "yes" << endl;
    else
      cout << "no" << endl;
  }
  return 0;
}

C++: #include <cstdio>
#include <iostream>
#include <algorithm>
#include <queue>
#include <stack>
#include <vector>
using namespace std;
const int maxx=100100;
vector<int> A[maxx];
int color[maxx];
int n,c=1;

void dfs(int u){
	if(color[u]!=-1) return ;//当该节点已经属于某一联通分量时，不需要染色
	color[u]=c;
	int si=A[u].size();
	for(int i=0;i<si;i++){
		if(color[A[u][i]]==-1){//注意是对A[u][i]进行染色
			dfs(A[u][i]);
		}
	}
	return ;
}

int main(){
	int q,a,b;//这里有个问题，n如果放在global里定义的话会出现问题，只能在main里定义，不知道为什么
	cin>>n>>q;
//	
//	cout<<&n<<endl<<&color<<endl<<&color[109]<<endl;
//	cout<<n<<endl;
	for(int i=0;i<=maxx;i++) color[i]=-1;
//	cout<<n<<endl;
	for(int i=1;i<=q;i++){
		cin>>a>>b;
		A[a].push_back(b);
		A[b].push_back(a);
	}
	for(int i=0;i<n;i++){
		dfs(i);
		c++;
	}
	cin>>q;
	for(int i=1;i<=q;i++){
		cin>>a>>b;
		if(color[a]==color[b]) cout<<"yes"<<endl;
		else cout<<"no"<<endl;
	}
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <map>
#include <stack>
using namespace std;

#define null -1

void DFS(vector<int> rVal[], map<int, int> &uColor_m, int idOrSs) {
	stack<int> stack;
	stack.push(idOrSs);
	uColor_m[idOrSs] = idOrSs;

	while (!stack.empty()) {
		int curUVal = stack.top();
		stack.pop();
		for (int i = 0; i < (signed)rVal[curUVal].size(); i++) {
			int curV = rVal[curUVal][i];
			if (uColor_m[curV] != null) continue;
			uColor_m[curV] = idOrSs;
			stack.push(curV);
		}
	}
}

void assignColor(int uNum, vector<int> rVal[], map<int, int> &uColor_m) {
	for (int i = 0; i < uNum; i++)
		uColor_m[i] = null;
	for (int i = 0; i < uNum; i++) {
		if (uColor_m[i] == null) DFS(rVal, uColor_m, i);
	}
}

int main() {
	int userNum;
	int relationNum;
//	int uColor_map[100000]; //<?????????, ??°??????????????????>
	map<int, int> uColor_m;
	//??????????????¨????????????
	vector<int> relationVal[100000];
	//int userColor[100000];

	cin >> userNum >> relationNum;
	for (int i = 0; i < relationNum; i++) {
		int userVal1, userVal2;
		cin >> userVal1 >> userVal2;
		relationVal[userVal1].push_back(userVal2);
		relationVal[userVal2].push_back(userVal1);
		uColor_m[i] = null;
	}

	assignColor(userNum, relationVal, uColor_m);

	int qNum;
	cin >> qNum;
	for (int i = 0; i < qNum; i++) {
		int uV1, uV2;
		cin >> uV1 >> uV2;
		if (uColor_m[uV1] == uColor_m[uV2])
			cout << "yes" << endl;
		else
			cout << "no" << endl;
	}
	return 0;
}

C++: #include <stdio.h>
#include <vector>
#include <algorithm>
#include <math.h>
#include <queue>

using namespace std;

int n,m,q,from,to;
int rank[100000],parent[100000];

int find(int x){
	if(x == parent[x])return x;
	else{
		return parent[x] = find(parent[x]);
	}
}

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

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

	if(x == y)return;

	if(rank[x] < rank[y]){
		parent[x] = y;
	}else{
		parent[y] = x;
		if(rank[x] == rank[y])rank[x]++;
	}
}

int main(){

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

	for(int i = 0; i < n; i++){
		rank[i] = 0;
		parent[i] = i;
	}

	for(int i = 0; i < m; i++){
		scanf("%d %d",&from,&to);

		if(isSame(from,to))continue;
		unite(from,to);
	}

	scanf("%d",&q);

	int left,right;

	for(int i = 0; i < q; i++){
		scanf("%d %d",&left,&right);

		if(isSame(left,right))printf("yes\n");
		else{
			printf("no\n");
		}
	}
	return 0;
}