Go: package main

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

const MAX = 100000

type Queue struct {
	head      int
	tail      int
	container [MAX]int
}

func (q *Queue) push(n int) {
	q.container[q.tail] = n
	q.tail = (q.tail + 1) % MAX
}

func (q *Queue) pop() int {
	res := q.container[q.head]
	q.head = (q.head + 1) % MAX
	return res
}

func (q *Queue) isEmpty() bool {
	return q.head == q.tail
}

var sc = bufio.NewScanner(os.Stdin)
var route [][]int
var SEEN [MAX]bool
var GROUP [MAX]int

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

func scanString() string {
	sc.Scan()
	return sc.Text()
}

func init() {
	sc.Split(bufio.ScanWords)
}

func bfs(start, group int) {
	que := Queue{}
	que.push(start)

	for !que.isEmpty() {
		id := que.pop()

		if SEEN[id] {
			continue
		}
		SEEN[id] = true
		GROUP[id] = group

		for _, next := range route[id] {
			que.push(next)
		}
	}
}

func main() {
	n, m := scanInt(), scanInt()
	route = make([][]int, n)
	for i := 0; i < m; i++ {
		s, t := scanInt(), scanInt()
		route[s] = append(route[s], t)
		route[t] = append(route[t], s)
	}

	for i := 0; i < n; i++ {
		if !SEEN[i] {
			bfs(i, i+1)
		}
	}

	w := bufio.NewWriter(os.Stdout)
	q := scanInt()
	for i := 0; i < q; i++ {
		s, t := scanInt(), scanInt()
		if GROUP[s] == GROUP[t] {
			fmt.Fprintln(w, "yes")
		} else {
			fmt.Fprintln(w, "no")
		}
	}
	w.Flush()
}

C++: #include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <math.h>

//============================================================================
#define pred(x) ((x)-1)
#define succ(x) ((x)+1)
#define True    1
#define False   0
//#define max(x,y) (((x)<(y))?y:x)
//============================================================================
#define MAX_BUFFER  102
struct graph{
    long id;
    unsigned char hands;
    unsigned char d;
    struct graph *gary[20];
};
typedef struct graph TGraph;
//============================================================================
unsigned char usedflags[100000];
short Stamp;
//============================================================================
void prnnode(TGraph *gptr)
{
    short j;

    printf("node=%d, hands=%d, ", gptr->id, gptr->hands);
    for (j=0; j<gptr->hands; j++)
        printf("%d ", gptr->gary[j]->id);
    printf("\n");
}
//----------------------------------------------------------------------------
void setflag(long n)
{
    usedflags[n>>3] |= 1<<(n & 0x7);
}
//----------------------------------------------------------------------------
int getflag(long n)
{
    return (usedflags[n>>3] & 1<<(n & 0x7));
}
//----------------------------------------------------------------------------
short search(TGraph *gptr, TGraph *fptr)
{
    short i;

    if (gptr==fptr)
        return True;
    //setflag(gptr->id);
    usedflags[gptr->id]=True;
#ifdef DESKTOP
   //prnnode(gptr);
#endif
    for (i=0; i<gptr->hands; i++){
        //if (!getflag(gptr->gary[i]->id)){
        if (!usedflags[gptr->gary[i]->id]){
            if (search(gptr->gary[i], fptr))
                return True;
        }
    }
    /*for (i=0; i<fptr->hands; i++){
        if (search(fptr->gary[i], gptr))
            return True;
    }*/
    return False;
}
//----------------------------------------------------------------------------
void addfrend(TGraph *gptr, TGraph *fptr)
{
    //TGraph **ptr; short i;

    //ptr=malloc(succ(gptr->hands)*sizeof(TGraph**));
    //for (i=0; i<gptr->hands; i++)
    //    ptr[i]=gptr->gary[i];

    //if (gptr->gary)
    //    free(gptr->gary);
    //gptr->gary=ptr;
    gptr->gary[gptr->hands++]=fptr;
}
//----------------------------------------------------------------------------
void filld(TGraph *gptr, long n)
{
    long i;

    for (i=0; i<n; i++)
        gptr[i].d=0;
}
//----------------------------------------------------------------------------
void input(FILE *file)
{
    long i,j,n,m,q,s,t; char buffer[20]; TGraph *graphary,*gptr,*fptr;

    fgets(buffer, sizeof(buffer)-1, file);
    sscanf(buffer, "%ld %ld", &n, &m);
    graphary=malloc(n*sizeof(TGraph));
    memset(graphary, 0, sizeof(TGraph));
    for (i=Stamp=0; i<m; i++){
        fscanf(file, "%ld", &s);
        fscanf(file, "%ld", &t);
        gptr=&graphary[s];
        fptr=&graphary[t];
        gptr->id=s;
        fptr->id=t;
        addfrend(gptr, fptr);
        addfrend(fptr, gptr);
    }
#ifdef DESKTOP
    for (i=m=0; i<n; i++){
        //prnnode(&graphary[i]);
        if (m<graphary[i].hands)
            m=graphary[i].hands;
    }
    setflag(0);
    printf("max hands = %d, %d\n", m, getflag(0));
#endif
    fscanf(file, "%ld", &q);
    for (i=0; i<q; i++){
        fscanf(file, "%ld", &s);
        fscanf(file, "%ld", &t);
        //filld(graphary, n);
        //memset(usedflags, 0, succ(n>>3));
        memset(usedflags, 0, n);
        printf("%s\n", (search(&graphary[s], &graphary[t]))?"yes":"no");
    }
}
//============================================================================
#ifndef DESKTOP
int main()
{
    input(stdin);
    return 0;
}
#endif

C++: #include <iostream>
#include <vector>
#include <unordered_set>
#include <algorithm>
//#include "../cxx-prettyprint/prettyprint.hpp"

std::vector<std::vector<int>> Adj;
std::unordered_set<int> nodes_visited;

bool is_reachable(int s, int t) {
    if (std::find(Adj[s].begin(), Adj[s].end(), t) != Adj[s].end()) {
        return true;
    } else if (nodes_visited.find(s) != nodes_visited.end()) {
        return false;
    } else {
        nodes_visited.insert(s);
        bool value = std::any_of(Adj[s].begin(), Adj[s].end(),
                                 [&](int next){return is_reachable(next, t);});
        return value;
    }
}

int main() {
    int n, m;
    std::cin >> n >> m;

    Adj.assign(n, std::vector<int>());
    for (int i = 0; i < m; i++) {
        int s, t;
        std::cin >> s >> t;
        Adj[s].push_back(t);
        Adj[t].push_back(s);
    }

    int q;
    std::cin >> q;
    for (int i = 0; i < q; i ++) {
        int s, t;
        std::cin >> s >> t;
        std::cout << (is_reachable(s, t) ? "yes" : "no") << std::endl;
    }
}

C++: #include <cstdint>
#include <vector>

using namespace std;

#define GRAPH_SIZE 100000

enum state_t {
  WHITE,
  GRAY,
  BLACK,
};

struct vertex_t {
  uint32_t color;
  vector<uint32_t> connections;
};

static vertex_t graph[GRAPH_SIZE];
static state_t state[GRAPH_SIZE];

static void colorize(uint32_t index, uint32_t color)
{
  if (state[index] == WHITE) {
    state[index] = GRAY;
    graph[index].color = color;
    for (uint32_t i = 0; i < graph[index].connections.size(); i++) {
      colorize(graph[index].connections[i], color);
    }
    state[index] = BLACK;
  }
}

void check_connection(size_t num)
{
  for (uint32_t i = 0; i < num; i++) {
    state[i] = WHITE;
  }

  uint32_t color = 1;
  for (uint32_t i = 0; i < num; i++) {
    colorize(i, color);
    color++;
  }
}

#include <iostream>

int32_t main()
{
  uint32_t n, m;
  cin >> n >> m;

  for (uint32_t i = 0; i < m; i++) {
    uint32_t index, to;
    cin >> index >> to;
    graph[index].connections.push_back(to);
    graph[to].connections.push_back(index);
  }

  check_connection(n);

  uint32_t qs;
  cin >> qs;

  for (uint32_t i = 0; i < qs; i++) {
    uint32_t from, to;
    cin >> from >> to;

    if (graph[from].color == graph[to].color) {
      cout << "yes" << endl;
    } else {
      cout << "no" << endl;
    }
  }

  return 0;
}