Go: package main

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

var (
	n     int
	G     [100000][]int
	color [100000]*int
)

func dfs(r int, c int) {
	S := Stack{}
	S.Push(r)
	color[r] = &c
	for !S.IsEmpty() {
		u := S.Pop()
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == nil {
				color[v] = &c
				S.Push(v)
			}
		}
	}
}

func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = nil
	}
	for u := 0; u < n; u++ {
		if color[u] == nil {
			id++
			dfs(u, id)
		}
	}
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Scan()
	n, _ = strconv.Atoi(sc.Text())
	sc.Scan()
	r, _ := strconv.Atoi(sc.Text())

	for i := 0; i < r; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}
	assignColor()
	sc.Scan()
	qNum, _ := strconv.Atoi(sc.Text())
	for i := 0; i < qNum; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

// Stack is Stack
type Stack struct {
	stack []int
}

// Push new value
func (stack *Stack) Push(val int) {
	stack.stack = append(stack.stack, val)
}

// Pop new value
func (stack *Stack) Pop() int {
	val := stack.stack[len(stack.stack)-1]
	stack.stack = stack.stack[0 : len(stack.stack)-1]
	return val
}

// IsEmpty return true when stack is empty
func (stack *Stack) IsEmpty() bool {
	return len(stack.stack) == 0
}

C++: #include<iostream>
using namespace std;
#include<stdio.h>

typedef struct box { int val; box *prev, *next; } box_t;

box_t* init()
{
    box_t* head = new box_t;
    head->val = -1;
    head->next = NULL;
    head->prev = NULL;
    return head;
}

box_t* make_tail(box_t* head)
{
    box_t* tail = new box_t;
    tail->val = -1;
    head->next = tail;
    tail->next = NULL;
    tail->prev = head;
    return tail;
}

bool isEmpty(box_t* head, box_t* tail)
{
    return (head->next == tail ? true : false);
}

box_t* f_insert(box_t* head, int data)
{
    box_t* box = new box_t;
    box->val = data;
    box->next = head->next;
    box->prev = head;
    head->next->prev = box;
    head->next = box;
    return box;
}

int b_pop(box_t* tail)
{
    if(!(tail->prev->prev)) return -1;
    box_t* box = tail->prev;
    int val;
    val = tail->prev->val;
    tail->prev = box->prev;
    box->prev->next = tail;
    delete box;
    return val;
}

void clear(box_t* head, box_t* tail)
{
    box_t* box1 = head->next;
    box_t* box2;
    if(box1 == tail) return;
    while(box1 != tail){
        box2 = box1->next;
        delete box1;
        box1 = box2;
    };
    head->next = tail;
    tail->prev = head;
    return;
}

int main()
{
    int G[100][100];
    int dist[100];

    box_t* head = init();
    box_t* tail = make_tail(head);

    int n, i, j, e, q, v1, v2;
    scanf("%d", &n);
    for(i = 0; i < n; i++){
        for(j = 0; j < n; j++){ G[i][j] = 0; } }
    int m;
    scanf("%d", &m);
    for(int k = 0; k < m; k++){
        scanf("%d %d", &i, &j);
        G[i][0]++; G[j][0]++;
        G[i][G[i][0]] = j;
        G[j][G[j][0]] = i;
    }
    scanf("%d", &q);
    int self, friends;
    bool is_connected;

    for(int k = 0; k < q; k++){
        for(j = 0; j < n; j++) dist[j] = -1;

        scanf("%d %d", &self, &friends);
        f_insert(head, self);
        dist[self] = 0;
        is_connected = false;

        while(1){
            v1 = b_pop(tail);
            e = G[v1][0];
            for(i = 1; i <= e; i++){
                v2 = G[v1][i];
                if(dist[v2] < 0){
                    dist[v2] = dist[v1] + 1;
                    f_insert(head, v2);
                }
            }
            if(dist[friends] > 0){
                is_connected = true;
                break;
            }
            if(isEmpty(head, tail)) break;
        };
        if(is_connected){ printf("yes\n"); }else{ printf("no\n"); }
        if(!isEmpty(head, tail)) clear(head, tail);
    }

    return 0;
}

C++: #include<iostream>
#include<cstring>

using namespace std;

int n,m,q,v[100005],color[100005];

struct edge{
    int index;
    edge *next;
};

struct head{
    int index;
    edge *first;
}heads[100005];

void dfs(int pre,int num,int c){
    v[num]=1;
    color[num]=c;
    edge *e=heads[num].first;
    while(e!=NULL){
        if(e->index!=pre&&v[e->index]==0)
            dfs(num,e->index,c);
        e=e->next;
    }
}

int main(){
    memset(v,0,sizeof(v));
    memset(color,0,sizeof(color));
    memset(heads,0,sizeof(heads));
    cin>>n>>m;
    int i,j,c=0;
    for(i=0;i<n;i++){
        heads[i].index=i;
    }
    for(i=0;i<m;i++){
        int a,b;
        cin>>a>>b;
        edge *e1=new edge();
        edge *e2=new edge();
        e1->index=b;
        e2->index=a;
        e1->next=heads[a].first;
        e2->next=heads[b].first;
        heads[a].first=e1;
        heads[b].first=e2;
    }
    for(i=0;i<n;i++){
        if(v[i]==0)dfs(-1,i,++c);
    }
    cin>>q;
    for(i=0;i<q;i++){
        int a,b;
        cin>>a>>b;
        if(color[a]==color[b])cout<<"yes"<<endl;
        else cout<<"no"<<endl;
    }
}

C++: #include<iostream>
#include<vector>
#include<stack>
using namespace std;
#define MAX 100000
#define 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=0;
    for(int i=0;i<n;i++)
    {
        color[i]=NIL;
    }
    for(int u=0;u<n;u++)
    {
        if(color[u]==NIL)dfs(u,id);
        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 <iostream>
#include <cstdio>
#include <cstdlib>
#include <cassert>
#include <string>
#include <cstring>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>

using namespace std;

// ---------------------
// repetition
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)

// debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

// ---------------------
#define INF 922337203685477580
typedef long long ll;
vector<int> par;

void init(int n) {
  par = vector<int>(n);
  REP(i, n) {
    par[i] = i;
  }
}
int root(int key) {
  if (par[key] == key) return key;
  return root(par[key]);
}
int same(int a, int b) {
  return root(a) == root(b);
}
void unite(int a, int b) {
  int x = root(a);
  int y = root(b);

  if (x == y) return;

  par[x] = y;
}

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

  init(n);

  REP(_, m) {
    int a, b;
    // cin >> a >> b;
    scanf("%d %d", &a, &b);
    unite(a, b);
  }
  int q;
  cin >> q;
  REP(_, q) {
    int a, b;
    // cin >> a >> b;
    scanf("%d %d", &a, &b);
    if (same(a, b)) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }

  return 0;
}