Go: package main

import (
	"fmt"
)

var n, m int
var g [][]int
var color []int

func main() {
	fmt.Scan(&n, &m)
	g = make([][]int, n) // SNSの関係を表すグラフ
	for i := 0; i < m; i++ {
		var a, b int
		fmt.Scan(&a, &b)
		g[a] = append(g[a], b) // 無向重みなしグラフ
		g[b] = append(g[b], a)
	}
	color = make([]int, n) // 各ノードにつける色
	for i := 0; i < len(color); i++ {
		color[i] = -1 // 初期化しておく
	}
	type query struct {
		s, t int
	}
	var Q int
	fmt.Scan(&Q)
	qs := make([]query, Q)
	for i := 0; i < Q; i++ {
		fmt.Scan(&qs[i].s, &qs[i].t)
	}
	// fmt.Println("n", n, "m", m, "g", g, "Q", Q, "qs", qs)
	// 全ての頂点からdfsする
	id := 1
	for u := 0; u < n; u++ {
		if color[u] == -1 {
			dfs(u, id)
			id++
		}
	}
	// fmt.Println("color", color)
	for i := 0; i < Q; i++ {
		if color[qs[i].s] == color[qs[i].t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func dfs(v, c int) {
	// fmt.Printf("dfs(v %d, c %d) en:\n", v, c)
	color[v] = c
	for _, vv := range g[v] {
		// fmt.Printf("  v %d, g[v] %v, vv %d\n", v, g[v], vv)
		if color[vv] == -1 {
			dfs(vv, c)
		}
	}
}

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;
}