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>
#include <stack>
using namespace std;
static const int MAX = 100000;
static const int NIL = -1;

int n;
vector<int> G[MAX];
int color[MAX];

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) {
        S.push(v);
        color[v] = c;
      }
    }
  }
}

void assignColor() {
  int id = 1;
  for (int i = 0; i < n; i++) {
    color[i] = NIL;
  }
  for (int i = 0; i < n; i++) {
    if (color[i] == NIL) {
      dfs(i, id++);
    }
  }
}

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

  assignColor();

  cin >> q;
  for (int i = 0; i < q; i++) {
    cin >> u >> v;
    if (color[u] == color[v]) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }

  return 0;
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
static const int MAX = 100000;
static const int NIL = -1;

int n;
vector<int> G[MAX];
int color[MAX];

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;
}

C++: #include <bits/stdc++.h>
using namespace std;

constexpr int MAX = 100010;

struct Edge{
    int v;
    Edge* next;
};

int N, M;
Edge* G[MAX];
int component[MAX];

void push( int u, int v ){
    Edge* e = new Edge;
    e->v = v;
    e->next = nullptr;

    Edge* i;
    for( i = G[u]; i->next != nullptr; i = i->next ){}
    i->next = e;
}

void dfs( int s, int k ){
    component[s] = k;
    for( Edge* e = G[s]->next; e != nullptr; e = e->next ){
        if( !component[e->v] ){
            dfs( e->v, k );
        }
    }
}

int main(){
    for( int i = 0; i < MAX; i++ ){
        Edge* e = new Edge;
        e->v = -1;
        e->next = nullptr;       
        G[i] = e;
    }
    
    cin >> N >> M;
    for( int i = 0; i < M; i++ ){
        int u, v; cin >> u >> v;
        push( u, v );
        push( v, u );
    }

    int k = 1;
    for( int i = 0; i < N; i++ ){
        if( !component[i] ){
            dfs( i, k );
            k++;
        }
    }

    int q; cin >> q;
    for( int i = 0; i < q; i++ ){
        int u, v; cin >> u >> v;
        if( component[u] == component[v] ){
            cout << "yes" << endl;
        }else{
            cout << "no" << endl;
        }
    }
}

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

void dfs(int node, std::vector<std::vector<int>>& v, std::vector<int>& colors, int color) {
    colors[node] = color;
    for (int i=0; i<v[node].size(); i++) {
        if (node != v[node][i] and colors[v[node][i]] == 0) {
            dfs(v[node][i], v, colors, color);
        }
    }
} 

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);
    int n, m, q, s, t, color=1;
    std::cin >> n >> m;
    std::vector<std::vector<int>> v(n);
    std::vector<int> colors(n);
    for (int i=0; i<m; i++) {
        std::cin >> s >> t;
        v[s].push_back(t);
        v[t].push_back(s);
    }
    for (int i=0; i<n; i++) {
        if (colors[i] == 0) {
            dfs(i, v, colors, color++);
        }
    }
    std::cin >> q;
    for (int i=0; i<q; i++) {
        std::cin >> s >> t;
        if (colors[s] == colors[t] and colors[s] != 0) {
            std::cout << "yes\n";
        } else {
            std::cout << "no\n";
        }
    }

    return 0;
}

C++: /*
* @Author: Samson
* @Date:   2018-05-07 21:12:41
* @Last Modified by:   Samson
* @Last Modified time: 2018-05-07 21:44:27
*/
//   @URL : 
#include<bits/stdc++.h>
#include<algorithm>
#include<vector>
#include<stack>
#include <cstdlib>
#define INF 0x3f3f3f3f
using namespace std;
typedef long long LL;
const int MAXN = 1e5+10;

int n,m,q,color[MAXN];
vector<int> v[MAXN];

void dfs(int x,int id)
{
	stack<int> s;
	int t;
	s.push(x);
	color[x] = id;
	while(s.size())
	{
		t = s.top();
		s.pop();
		for(int i = 0; i < v[t].size(); ++i)
		{
			int val = v[t][i];
			if(color[val] == -1)
			{
				color[val] = id;
				s.push(val);
			}
		}
	}
}

void fun()
{
	int id = 0;
	memset(color,-1,sizeof color);
	for(int i = 0; i < n; ++i)
		if(color[i] == -1)
			dfs(i,++id);
}

int main(void)
{
	ios::sync_with_stdio(false); 
	//cin.tie(0);
	cin>>n>>m;
	int s,e;
	for(int i = 0; i < m; ++i)
	{
		cin>>s>>e;
		v[s].push_back(e);
		v[e].push_back(s);
	}
	fun();
	cin>>q;
	while(q--)
	{
		cin>>s>>e;
		if(color[s] == color[e] && color[s]!=-1)
			cout<<"yes\n";
		else
			cout<<"no\n";
	}
	return 0;
}