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 "bits/stdc++.h"
#include <unordered_set>

#define _CRT_SECURE_NO_WARNINGS

#define REP(i, n) for(decltype(n) i = 0; i < (n); i++)
#define REP2(i, x, n) for(decltype(x) i = (x); i < (n); i++)
#define REP3(i, x, n) for(decltype(x) i = (x); i <= (n); i++)
#define RREP(i, n) for (decltype(n) i = (n) - 1; i >= 0; i--)

#define ALL(a) (a).begin(),(a).end()
#define SORT(c) sort((c).begin(),(c).end())
#define DESCSORT(c) sort(c.begin(), c.end(), greater<int>())

using namespace std;

const int INF = 1000000000;
const double PI = 3.1415926535897932384626433832795;

// N, E, S, W
const int dx[4] = { -1, 0,  1,  0 };
const int dy[4] = { 0, 1,  0, -1 };

using LL = long long int;
using LD = long double;
using pii = pair<int, int>;
using pdd = pair<double, double>;
using pll = pair<LL, LL>;
using vi = vector<int>;
using vd = vector<double>;
using vll = vector<LL>;
using vs = vector<string>;
using vvi = vector<vi>;

//==============================================
int n, m, q;
vi color;
vvi G;

void antDfs(int r, int teamNum) {
	stack<int>S;
	S.push(r);
	color[r] = teamNum;
	while (!S.empty()) {
		int u = S.top(); S.pop();
		REP(i, G[u].size()) {
			int v = G[u][i];
			if (color[v] == -1) {
				color[v] = teamNum;
				S.push(v);
			}
		}
	}
}

void func() {
	int id = 1;
	REP(i, n) {
		if (color[i] == -1) {
			antDfs(i, id++);
		}
	}
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	cin >> n >> m;

	color.resize(n, -1);
	G.resize(n);

	int a, b;
	REP(i, m) {
		cin >> a >> b;
		G[a].push_back(b);
		G[b].push_back(a);
	}

	func();


	cin >> q;

	REP(i, q) {
		cin >> a >> b;
		if (color[a] == color[b]) {
			cout << "yes" << "\n";
		} else {
			cout << "no" << "\n";
		}
	}
	return 0;
}

C++: /*
 * d.cc: 
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>

using namespace std;

/* constant */

const int MAX_N = 100000;
const int INF = 1 << 30;

/* typedef */

typedef vector<int> vi;
typedef queue<int> qi;

/* global variables */

vi nbrs[MAX_N];
int ids[MAX_N];

/* subroutines */

/* main */

int main() {
  int n, m;
  cin >> n >> m;

  for (int i = 0; i < m; i++) {
    int u, v;
    cin >> u >> v;
    nbrs[u].push_back(v);
    nbrs[v].push_back(u);
  }

  int gn = 0;

  for (int st = 0; st < n; st++)
    if (! ids[st]) {
      ids[st] = ++gn;
      qi q;
      q.push(st);

      while (! q.empty()) {
	int u = q.front(); q.pop();
	vi &nbru = nbrs[u];

	for (vi::iterator vit = nbru.begin(); vit != nbru.end(); vit++) {
	  int &v = *vit;
	  if (! ids[v]) {
	    ids[v] = gn;
	    q.push(v);
	  }
	}
      }
    }

  int qn;
  cin >> qn;
  while (qn--) {
    int s, t;
    cin >> s >> t;
    cout << (ids[s] == ids[t] ? "yes" : "no") << endl;
  }
  return 0;
}

C++: #include<cstdio>
#include<cstdlib>
#include<cstring>
#include<vector>
using namespace std;
vector<int> neighbors[100005];
//why choose vector, not matrix
int root[100005];

void dfs(int i, int start){
	root[i] = start;
	//visut all i's neighbors
	//c++ 11
	for(int j : neighbors[i]){
		if(root[j]==-1){
			dfs(j,start);
		}
	}
}

int main(){
	int n,m,x,y;
	memset(root, -1, sizeof(root));
	scanf("%d %d",&n,&m);
	for(int i = 0; i<m; i++){
		scanf("%d %d",&x,&y)
		neighbors[x].push_back(y);
		neighbors[y].push_back(x);
	}
	for(int i = 0; i<n; i++){
		if(root[x]= -1){
			dfs(i,i);
		}
	}
	scanf("%d", &q);
	for(int i = 0; i<q; i++){
		scanf("%d %d",&x, &y);
		if(root[x] = root[y]){
			printf("Yes\n");
		}else printf("no\n");
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
using namespace std;
int a[100000],gp[1000000],g=0;
int inf=100000,n,m;
vector< vector<int> > v(100000);
void dfs(int s){
    gp[s]=g;
    a[s]=inf;
    for(int i=0;i<(int)v[s].size();i++){
        if(a[v[s][i]]!=inf){
            dfs(v[s][i]);
        }
    }
}
int main(){
  cin>>n>>m;
  for(int i=0;i<m;i++){
      int tmp,u;
      cin>>tmp>>u;
      v[tmp].push_back(u);
      v[u].push_back(tmp);
  }
  dfs(0);
  for(int i=0;i<n;i++){
      g++;
      if(!a[i])dfs(i);
  }
  int qu;
  cin>>qu;
  int s[qu],t[qu];
  for(int i=0;i<qu;i++)cin>>s[i]>>t[i];
  for(int i=0;i<qu;i++){
      if(gp[s[i]]==gp[t[i]])
          cout<<"yes\n";
      else
          cout<<"no\n";
  }
}