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++: // include
//------------------------------------------
#include <bits/stdc++.h>

using namespace std;

// conversion
//------------------------------------------
inline int toInt(string s) {
    int v;
    istringstream sin(s);
    sin >> v;
    return v;
}
template <class T>
inline string toString(T x) {
    ostringstream sout;
    sout << x;
    return sout.str();
}

// math
//-------------------------------------------
template <class T>
inline T sqr(T x) {
    return x * x;
}

// typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;

// container util
//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i, c) \
    for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())

// repetition
//------------------------------------------
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)
#define REPI(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)

// constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI = acos(-1.0);
const int INF_INT = 2147483647;
const LL INF_LL = 9223372036854775807;

// clear memory
//--------------------------------------------
#define CLR(a) memset((a), 0, sizeof(a))

// vector
//--------------------------------------------
template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (T &x : vec) is >> x;
    return is;
}

// pair
//--------------------------------------------
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
    os << "(" << pair_var.first << ", " << pair_var.second << ")";
    return os;
}

// vector
//--------------------------------------------
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &vec) {
    os << "{";
    for (int i = 0; i < vec.size(); i++) {
        os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
    }
    os << "}";
    return os;
}

// list
//--------------------------------------------
template <typename T>
ostream &operator<<(ostream &os, const list<T> &lst) {
    os << "{";
    REPI(itr, lst) {
        os << *itr;
        itr++;
        if (itr != lst.end()) os << ", ";
        itr--;
    }
    os << "}";
    return os;
}

// map
//--------------------------------------------
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
    os << "{";
    REPI(itr, map_var) {
        os << *itr;
        itr++;
        if (itr != map_var.end()) os << ", ";
        itr--;
    }
    os << "}";
    return os;
}

// set
//--------------------------------------------
template <typename T>
ostream &operator<<(ostream &os, set<T> &set_var) {
    os << "{";
    REPI(itr, set_var) {
        os << *itr;
        itr++;
        if (itr != set_var.end()) os << ", ";
        itr--;
    }
    os << "}";
    return os;
}

// dump
//--------------------------------------------
#define DUMPOUT cerr

void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&... tail) {
    DUMPOUT << head;
    if (sizeof...(Tail) > 0) {
        DUMPOUT << ", ";
    }
    dump_func(std::move(tail)...);
}
#ifdef DEBUG_
#define DEB
#define dump(...)                                                       \
    DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                     \
            << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" \
            << endl                                                     \
            << "    ",                                                  \
        dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif

static const int MAX = 100000;
static const int NIL = -1;

int n;
VI g[MAX];
int cl[MAX];

void dfs(int r, int c) {
    stack<int> s;
    s.push(r);
    cl[r] = c;
    while (!s.empty()) {
        int u = s.top();
        s.pop();
        REP(i, g[u].size()) {
            int v = g[u][i];
            if (cl[v] == NIL) {
                cl[v] = c;
                s.push(v);
            }
        }
    }
}

void assignColor() {
    int id = 1;
    REP(i, n) cl[i] = NIL;
    REP(u, n) if (cl[u] == NIL) dfs(u, id++);
}

int main(int argc, char *argv[]) {
    cin >> n;
    int m;
    cin >> m;
    REP(i, m) {
        int s, t;
        cin >> s >> t;
        g[s].PB(t);
        g[t].PB(s);
    }
    assignColor();
    int q;
    cin >> q;
    REP(i, q) {
        int s, t;
        cin >> s >> t;
        if (cl[s] == cl[t])
            cout << "yes";
        else
            cout << "no";
        cout << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <queue>
using namespace std;
struct Node{
    vector<int> fri;
    bool flag;
};
queue<Node> refresh(queue<Node> que,Node node[],int n){
    while(!que.empty())
        que.pop();
    
    for(int i=0; i<n; i++)
        node[i].flag=false;

    return que;
}

int main(){
    int n,m,s,t;
    Node node[100000];
    cin >> n >> m;

    for(int i=0; i<m; i++){
        cin >> s >> t;

        node[s].fri.push_back(t);
        node[t].fri.push_back(s);
    }

    queue<Node> que;
    refresh(que,node,n);

    int q;
    cin >> q;

    bool answer[10000];
    for(int i=0; i<q; i++){
        answer[i]=false;
        cin >> s >> t;

        node[s].flag=true;
        que.push(node[s]);

        while(!que.empty() && !answer[i]){
         Node fro = que.front();

         for(int j=0; j<fro.fri.size(); j++){
            int x = fro.fri[j];
  
            if(x==t){
                answer[i]=true;
                break;
            }

            if(!node[x].flag){
                node[x].flag=true;
                que.push(node[x]);
            }
         }

          que.pop();
        }

        que=refresh(que,node,n);
    }

    for(int i=0; i<q; i++){
        if(answer[i])
            cout << "yes\n";
        else
            cout << "no\n";
    }
}