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 <cassert>
#include <cstdio>
#include <algorithm>
#include <iostream>
#include <vector>
#include <list>

class TVertex
{
    int FIndex;
    int FCommuniyId;
    std::list<TVertex*> FList;

public:
    TVertex(int Index)
     : FIndex(Index), FCommuniyId(0)
    {}
    void AddPath(TVertex* Vertex)
    {
        FList.push_back(Vertex);
    }
    void SetCommunity(int CommunityId)
    {
        if(FCommuniyId) return;
        FCommuniyId = CommunityId;
        for(std::list<TVertex*>::iterator It = FList.begin(); It != FList.end(); ++It){
            TVertex* V = *It;
            V->SetCommunity(CommunityId);
        }
    }
    int CommunityId()const
    {
        return FCommuniyId;
    }
};
class TGraph
{
    std::vector<TVertex*> FTable;
    void Init(int n)
    {
        assert(n > 0);
        FTable.resize(n);
        for(int i = 0; i < n; ++i){
            FTable[i] = new TVertex(i);
        }
    }
public:
    TGraph(int n)
    {
        Init(n);
    }
    void MakeFriend(int s, int t)
    {
        assert(s < FTable.size());
        assert(t < FTable.size());
        FTable[s]->AddPath(FTable[t]);
        FTable[t]->AddPath(FTable[s]);
    }
    void SetCommunity()
    {
        for(std::size_t i = 0; i < FTable.size(); ++i){
            FTable[i]->SetCommunity(i+1);
        }
    }
    bool IsSameCommunity(int s, int t)const
    {
        assert(s < FTable.size());
        assert(t < FTable.size());
        return FTable[s]->CommunityId() == FTable[t]->CommunityId();
    }
};

int main()
{
    int n, m;
    std::scanf("%d %d", &n, &m);
    TGraph Graph(n);
    for(int i = 0; i < m; ++i){
        int s, t;
        std::scanf("%d %d", &s, &t);
        Graph.MakeFriend(s, t);
    }
    int q;
    std::scanf("%d", &q)
    Graph.SetCommunity();
    for(int i = 0; i < q; ++i){
        int s, t;
        std::scanf("%d %d", &s, &t);
        std::printf("%s\n", (Graph.IsSameCommunity(s, t) ? "yes" : "no"));
    }
    return 0;
    
}

C++: #include<stdio.h>
#include<vector>
using namespace std;

vector<vector<int> >g;
int n,m,q,s,t;

vector<bool>visited;
vector<int>color;
void dfs(int s){
    for(int i=0;i<g[s].size();i++){
        if(color[g[s][i]]==-1){
            color[g[s][i]]=color[s];
            dfs(g[s][i]);
        }
    }
}
int main() {
    scanf("%d %d",&n,&m);
    g.resize(n);
    color.resize(n,-1);
    for(int i=0;i<m;i++){
        scanf("%d %d",&s,&t);
        g[s].push_back(t);
    }
    for(int i=0;i<n;i++){
        if(color[i]==-1){
            color[i]=i;
            dfs(i);
        }
    }
    scanf("%d",&q);
    for(int i=0;i<q;i++){
        scanf("%d %d",&s,&t);
        printf((color[s]==color[t]?"yes\n":"no\n"));
    }
    return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;
int main()
{
    int n, m, q;
    scanf("%d %d", &n, &m);
    vector<vector<int> > a(n, vector<int>(0));
    for (int i = 0, j, k; i < m; i++)
    {
        scanf("%d %d", &j, &k);
        a[j].push_back(k);
        a[k].push_back(j);
    }
    vector<int> vis(n, -1);
    for (int i = 0; i < n; i++)
    {
        
        if (vis[i] == -1)
        {
            stack<int> b;
            b.push(i);
            vis[i] = i;
            for (int t; !b.empty(); )
            {
                t = b.top();
                b.pop();
                for (int j = 0; j < a[t].size(); j++)
                {
                    
                    if (vis[a[t][j]] == -1)
                    {
                        vis[a[t][j]] = i;
                        b.push(a[t][j]);
                    }
                }
            }
        }
    }
    
    scanf("%d", &q);
    for (int i = 0, j, k; i < q; i++)
    {
        scanf("%d %d", &j, &k);
        printf(vis[j] == vis[k] ? "yes\n" : "no\n");
    }
}