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++: /* ALDS1_11_D: Connected Components */

#include <iostream>
#include <vector>
#include <stack>
using std::vector;
using std::stack;

void grouping(int id, int group_id, int group_ids[], vector<int> sns[]) {
    stack<int> S;
    S.push(id);
    group_ids[id] = group_id;

    while(! S.empty()) {
        id = S.top();
        S.pop();
        vector<int> friends = sns[id];
        for (int i = 0; i < friends.size(); i++) {
            int friend_id = friends[i];
            if (group_ids[friend_id] < 0) {
                group_ids[friend_id] = group_id;
                S.push(friend_id);
            }
        }
    }
}

void assign_groups(int n_users, vector<int> sns[], int group_ids[]) {
    int group_id = 0;
    std::fill_n(group_ids, n_users, -1);
    for (int id = 0; id < n_users; id++) {
        if (group_ids[id] < 0) {
            grouping(id, group_id, group_ids, sns);
            group_id++;
        }
    }
}

int main() {
    std::ios::sync_with_stdio(false);

    int n_users, n_relations;
    std::cin >> n_users >> n_relations;

    int id, friend_id, n_friends;
    vector<int> *sns = new vector<int>[n_users];
    for (int i = 0; i < n_relations; i++) {
        std::cin >> id >> friend_id;
        sns[id].push_back(friend_id);
        sns[friend_id].push_back(id);
    }

    int group_ids[n_users];
    assign_groups(n_users, sns, group_ids);

    int n_questions;
    std::cin >> n_questions;

    for (int i = 0; i < n_questions; i++) {
        std::cin >> id >> friend_id;
        bool same_group = group_ids[id] == group_ids[friend_id];
        std::cout << ( same_group ? "yes" : "no" ) << "\n";
    }
    return 0;
}

C++: #include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <queue>
#include <vector>
using namespace std;

const int maxn = 100000 + 5;
int color[maxn];
bool vis[maxn];
vector <int> G[maxn];

void dfs(int u, int c)
{
    vis[u] = true;
    color[u] = c;

    for (int i = 0; i < G[u].size(); i++)
        if (!vis[G[u][i]])
        dfs(G[u][i], c);
}

int main()
{
    int n, m;
    while (scanf("%d %d", &n, &m) != EOF)
    {
        for (int i = 0; i < n; i++)
            G[i].clear();

        int u, v;
        for (int i = 0; i < m; i++)
        {
            scanf("%d %d", &u, &v);
            G[u].push_back(v);
            G[v].push_back(u);
        }

        memset(color, 0, sizeof(color));
        memset(vis, false, sizeof(vis));

        int c = 0;
        for (int i = 0; i < n; i++)
        {
            if (!vis[i])
            {
                ++c;
                dfs(i, c);
            }
        }

        int q;
        scanf("%d", &q);
        while (q--)
        {
            int u, v;
            scanf("%d %d", &u, &v);
            if (color[u] == color[v])
                printf("yes\n");
            else
                printf("no\n");
        }
    }
    return 0;
}

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

const int N = 10000;
const int WHITE = 0;
const int GRAY = 1;
const int BLACK = 2;
const int NIL = -1;

int n, M[N][N];
int color[N], cc[N], cp = 0;
int nt[N];

int next(int u){
	for (int v = nt[u]; v <= n; v++){
		nt[u] = v + 1;
		if (M[u][v]) return v;
	}
	return NIL;
}

void dfs_visit(int r){
	for (int i = 0; i < n; i++) nt[i] = 0;

	stack<int> S;
	S.push(r);
	color[r] = GRAY;
	cc[r] = cp;

	while (!S.empty()){
		int u = S.top();
		int v = next(u);
		if (v != NIL){
			if (color[v] == WHITE){
				color[v] = GRAY;
				cc[v] = cp;
				S.push(v);
			}
		}
		else {
			S.pop();
			color[u] = BLACK;
		}
	}
	cp++;
}

void dfs(){
	for (int i = 0; i < n; i++){
		color[i] = WHITE;
		nt[i] = 0;
	}

	for (int u = 0; u < n; u++){
		if (color[u] == WHITE) dfs_visit(u);
	}

}

int main(){
	int m, q;
	cin >> n >> m;
	for (int i = 0; i < n; i++){
		for (int j = 0; j < n; j++) M[i][j] = 0;
	}
	for (int i = 0; i < m; i++){
		int s, t;
		cin >> s >> t;
		M[s][t] = M[t][s] = 1;
	}

	dfs();

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

	return 0;
}