Go: package main

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

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	nNodes := scanInt(sc)
	nConns := scanInt(sc)

	graph := make([][]int, nNodes)
	for i := 0; i < nConns; i++ {
		a, b := scanInt(sc), scanInt(sc)
		graph[a] = append(graph[a], b)
		graph[b] = append(graph[b], a)
	}

	groups := make([]int, nNodes)

	var setGroups func(int, int)
	setGroups = func(u int, groupId int) {
		if groups[u] > 0 {
			return
		}
		groups[u] = groupId

		for _, v := range graph[u] {
			setGroups(v, groupId)
		}
	}
	for i := 0; i < nNodes; i++ {
		setGroups(i, i+1)
	}

	nQuestions := scanInt(sc)

	w := bufio.NewWriter(os.Stdout)
	var ans string
	for i := 0; i < nQuestions; i++ {
		a, b := scanInt(sc), scanInt(sc)
		if groups[a] == groups[b] {
			ans = "yes"
		} else {
			ans = "no"
		}
		fmt.Fprintln(w, ans)
	}
	w.Flush()
}

func scanInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

C++: ////////////////////////////////////////
//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 = 2e9-1;

int color[100010];


int find(int i) {
    if(color[i] == i) return i;
    
    return color[i] = find( color[i] );
}


void unioN(int x, int y) {
    x = find(x);
    y = find(y);
    
    color[x] = y;
}


bool isLinked(int x, int y) {
    return find(x) == find(y);
}



int main() {
    int N; din >> N;
    int M; din >> M;
    
    //initialize
    rep(i,0,N) {
        color[i] = i;
    }
    
    //read input data
    int x, y;
    rep(i,0,M) {
        din >> x >> y;
        unioN(x, y);
        
        
//        //test display
//        dout << "--------------------\n";
//        dout << "unioN " << x << " " << y << endl;
//        rep(j,0,N) {
//            disP(j); disp(color[j]);
//        }
    }
    
    
    //output
    int Q; din >> Q;
    rep(i,0,Q) {
        din >> x >> y;
        
        
        //test display
//        dout << "--------------------\n";
//        dout << "isLinked " << x << " " << y << endl;
        
        dout << ( isLinked(x, y) ? "yes" : "no" ) << endl;
        
//        rep(j,0,N) {
//            disP(j); disp(color[j]);
//        }
    }
    
    
    
    
#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;

vector<int> G[10000];
int color[10000];
int n;

void dfs(int idx, int c)
{
	stack<int> s;
	s.push(idx);
	color[idx] = 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] == -1)
			{
				color[v] = c;
				s.push(v);
			}
		}
	}
}

void AssignColor()
{
	int id = 1;
	for (int i = 0; i < n; ++i) color[i] = -1;
	for (int u = 0; u < n; ++u)
	{
		if (color[u] == -1) 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;
}