Go: package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N, M := sc.nextInt(), sc.nextInt()
	G := make([][]int, N)
	for i := 0; i < M; i++ {
		s, t := sc.nextInt(), sc.nextInt()
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}
	group := make([]int, N)
	for i := 0; i < N; i++ {
		group[i] = -1
	}
	var dfs func(cur int)
	dfs = func(cur int) {
		for i := 0; i < len(G[cur]); i++ {
			next := G[cur][i]
			if group[next] == -1 {
				group[next] = group[cur]
				dfs(next)
			}
		}
	}
	num := 0
	for i := 0; i < N; i++ {
		if group[i] == -1 {
			group[i] = num
			dfs(i)
			num++
		}
	}

	Q := sc.nextInt()
	for i := 0; i < Q; i++ {
		s, t := sc.nextInt(), sc.nextInt()
		if group[s] == group[t] {
			fmt.Fprintln(wtr, "yes")
		} else {
			fmt.Fprintln(wtr, "no")
		}
	}
	wtr.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;
    }
}