Go: // AOJ ALDS1_11_D: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_11_D

package main

import (
	"bufio"
	"container/list"
	"fmt"
	"os"
	"strconv"
)

var nocolor = -1

type graph struct {
	graph  [][]int
	colors []int
}

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

func newGraph(nodeNum int) *graph {
	colors := make([]int, nodeNum)
	g := make([][]int, nodeNum)
	for i := 0; i < nodeNum; i++ {
		g[i] = []int{}
		colors[i] = nocolor
	}

	return &graph{g, colors}
}

func constructGraph(sc *bufio.Scanner) *graph {
	usersNum := nextInt(sc)
	linkNum := nextInt(sc)

	g := newGraph(usersNum)
	for i := 0; i < linkNum; i++ {
		u := nextInt(sc) // node
		l := nextInt(sc) // link node
		// edge each other
		g.graph[u] = append(g.graph[u], l)
		g.graph[l] = append(g.graph[l], u)
	}
	return g
}

func (g *graph) dfs(r, color int) {
	g.colors[r] = color

	stack := list.New()
	stack.PushFront(r)

	for stack.Len() > 0 {
		v := stack.Remove(stack.Front()).(int)
		for _, u := range g.graph[v] {
			if g.colors[u] == nocolor {
				g.colors[u] = color
				stack.PushFront(u)
			}
		}
	}
}

func (g *graph) assignColor() {
	color := 1
	for u := 0; u < len(g.graph); u++ {
		if g.colors[u] == nocolor {
			g.dfs(u, color)
			color++
		}
	}
}

func (g *graph) isLink(s, t int) bool {
	return g.colors[s] == g.colors[t]
}

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

	// construct graph and friendly colors
	g := constructGraph(sc)
	g.assignColor()

	// judge link
	q := nextInt(sc)
	for i := 0; i < q; i++ {
		s := nextInt(sc)
		t := nextInt(sc)

		if g.isLink(s, t) {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

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;
}