Go: package main

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

func main() {
	var n,m int
	fmt.Scan(&n)
	group := make([]int, n)
	g := make([][]int, n)
	for i := 0; i < n; i++ {
		g[i] = []int{}
		group[i] = -1
	}
	
	fmt.Scan(&m)
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	for i := 0; i < m; 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)
	}
	for i := 0; i < n; i++ {
		if group[i] != -1 {
			continue
		}
		q := []int{i}
		for len(q) > 0 {
			pop := q[0]
			if len(q) > 1 {
				q = q[1:]
			} else {
				q = []int{}
			}
			if group[pop] == -1 {
				q = append(q, g[pop]...)
				group[pop] = i
			}
		}
	}
	sc.Scan()
	q, _ := strconv.Atoi(sc.Text())
	for i := 0; i < q; i++ {
		sc.Scan()
		s, _ := strconv.Atoi(sc.Text())
		sc.Scan()
		t, _ := strconv.Atoi(sc.Text())

		if group[s] == group[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func root(i int, group *[]int) int {
	if i == (*group)[i] {
		return i
	}
	(*group)[i] = root((*group)[i], group)
	return (*group)[i]
}

C++: ////////////////////////////////////////
//??°??????????????????
//ALDS1_11_A:   Graph
//ALDS1_11_B:   Depth First Search
//ALDS1_11_C:   Breadth First Search
//????????§????????\?????????????£?
//
//ALDS1_11_D:   Connected Components
//
////////////////////////////////////////

#include <iostream>
#include <algorithm> // next_permutation
#include <iomanip>
#include <cmath>
#include <vector>
#include <sstream>
#include <string>
#include <cstdio>
#include <stack>
#include <queue>
#include <list>
#include <numeric> //accumulate
//#include <unordered_map> //???????????\??¢??°
#include <fstream> //ifstream, ofstream

//#define NDEBUG //NDEBUG???#include <cassert>???????????????????????????????????´???assert?????????????????????????????????NDEBUG?????????????????????????????????????????????
#include <cassert> //assert


using namespace std;

//???????????°??????TEST????????????????????¬???????????????????????????????????¢????????????
#define TEST //*******************************************************************************************************************************************
//?????????????????¨??§?????\????????????????????????????????°?????????????¨???????????????????dout???????????????????????§???????????¬??????????????????????????????????????????
//??????????????????????????????????????????????????????????§?CPU???????£??????????????????§???TLE?????????????????????????????????????????§????????¨???                           ????????????????????????cerr????????£????????????????????????????????????
#ifdef TEST
#define dout cout
#define din cin
#else
stringstream dummy; //???????????°??????dout?????????????????????????????????
#define dout dummy.str(""); dummy.clear(stringstream::goodbit); dummy //dummy?????????????????????????????????????????¨?????¢?????¢???????????????
//???????????¨??????????????????goodbit?????????????????????????????¨???????????´????????????????????????????????¨?????°?????????????????§???????????????????????????????????? http://d.hatena.ne.jp/linden/20060427/p1
#endif

//?¨??????????????????????????????????????????????????????´??????OUTPUTFILE????????????????????¬???????????????????????????????????¢????????????
//#define OUTPUTFILE "output.txt" //*******************************************************************************************************************************************
#ifdef OUTPUTFILE
#define dout outputfile //??¨????????????TLE????????§?????????dout?????¨??¨??????????????¢????????????????????????????????????????????§????¨????????????´??????????????£??????????????????????¨?????????????????????????????????????????????§?????????????????????
ofstream outputfile(OUTPUTFILE);
#define OutputFilePath "/Users/Nag/Documents/Prgm/Test/DerivedData/Test/Build/Products/Debug/output.txt"
#endif

//?¨??????\???????????????????????????????????????????????´??????INPUTFROMTEXTFILE????????????????????¬???????????????????????????????????¢????????????
//#define INPUTFILE "input.txt" //*******************************************************************************************************************************************
#ifdef INPUTFILE
#define din inputfile
ifstream inputfile(INPUTFILE);
#endif


#define disp(A) dout << #A << " = " << (A) << endl
#define disP(A) dout << setw(3) << (A) << " " // << setw(3) ??????????????\????????????
#define rep(i,a,n) for(int (i)=(a); (i)<(n); (i)++)
#define dispAll(A,n) dout << #A << " = "; rep(j, 0, (n)) {disP(A[j]);} dout << endl

typedef pair<int,int> pii;
typedef vector<int> vi;
typedef unsigned long long ll;


const int INF = 1e9-1;

const int N_MAX = 100000;

bool edge[N_MAX][N_MAX] = {0};
int color[N_MAX] = {0}; //??£?????°???????????¨???1??\????????°?????§???????????????
int currentColor = 0;

int NN = 0;


void dfs(int i) { //depth first search
    
    if(color[i]!=0) return; //?????§????¨??????????
    
    //??????????????????????¨??????§????????°?????????????????????????????????????????????????????????dfs????????°??????????????????
    color[i] = currentColor;
    rep(j,0,NN) {
        if(edge[i][j]) dfs(j);
    }
    
    //???????????????????????????dfs??????????????????????????????????????£??????
    return;
    
}



int main() {
    int M;
    din>>NN>>M;
    
    int v1, v2;
    rep(i,0,M) {
        din>>v1>>v2;
        edge[v1][v2] = edge[v2][v1] = 1;
    }
    
    rep(i,0,NN) edge[i][i] = 1;
    
    
    
//    //test display
//    dout<<endl;
//    dout<<"       dist = ";
//    rep(i,0,NN) disP(i);
//    dout<<endl;
//    rep(i,0,NN) {
//        disP(i); dispAll(edge[i], NN);
//    }
//    dout<<endl;
    
//    //test display
//    dout<<"    i = ";
//    rep(i,0,NN) disP(i);
//    dout << endl;
//    dispAll(color, NN);
    
    
    //execute DFS (Depth First Search)
    //??±???????????¢?´¢??§??¨??????????????¢?´¢?????????????????°?????????????????????????£??????????????????????????????????
    rep(i,0,NN) {
        if(color[i]==0) { //?????????????????????????????????dfs
            currentColor++;
            dfs(i);
        }
    }
    
//    //test display
//    dout<<"    i = ";
//    rep(i,0,N) disP(i);
//    dout << endl;
//    dispAll(color, N);
    
    //output
    int Q; din>>Q;
    rep(i,0,Q) {
        din >> v1 >> v2;
        
        dout << (color[v1]==color[v2] ? "yes" : "no") << endl;
    }
    
    
    
#ifdef INPUTFILE
    inputfile.close();
#endif
    
#ifdef OUTPUTFILE
    outputfile.close();
    cout << "\"" << OutputFilePath << "\"" << endl;
#endif
    
    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;
}