C++ :

#include<iostream>
#include<cstring>
#include<queue>
#include<cstdio>
using namespace std;
bool a[110][110];
bool flag[110];
int n,e;
void init();
void bfs(int x);
int main()
{
	//freopen("bfs5.in","r",stdin);
	//freopen("bfs5.out","w",stdout);
	init();
	bfs(1);
	return 0;
}
void init()
{
	cin>>n>>e;
	memset(flag,0,sizeof(flag));
	memset(a,0,sizeof(a));
	int x,y;
	for(int i=1;i<=e;++i)
	{
		cin>>x>>y;
		a[x][y]=1;//无向图处理双向 
		a[y][x]=1;
	}
}
void bfs(int x)
{
	queue<int> q;
	cout<<x<<' ';
	flag[x]=1;//把遍历点设为已访问 
	q.push(x);//把当前点进队 
	while(!q.empty())//当队列非空	
	{
		for(int i=1;i<=n;i++)
		{
			if(!flag[i]&&a[q.front()][i])//遍历队首元素的相邻点 
			{
				cout<<i<<' ';//如果连通且没访问过进队 
				flag[i]=1;//一定要记得设访问标记，否会是死循环 
				q.push(i);
			}
		}
		q.pop();
	}
}

Pascal :

program acm21183;
const maxn=100;
type node=record
          u,v,next:longint;
          end;
var
  q:array[1..10000] of longint;
  num,i,j,k,n,e,u,v,x:longint;
  graph:array[1..maxn,1..maxn] of longint;
  vis:array[1..maxn] of boolean;
procedure bfs;
var
  i,f,r:longint;
begin
   f:=0; r:=1;
   q[1]:=1; vis[1]:=true;
   while f<r do
    begin
     inc(f);
     x:=q[f];
     if k=0 then begin write(x); k:=k+1 end
     else write(' ',x);
     for i:=1 to n do
      if (not vis[i]) and (graph[x,i]>0) then
        begin
          graph[x,i]:=0;
          graph[i,x]:=0;
          vis[i]:=true;
          inc(r);
          q[r]:=i;
        end;
     end;
end;
procedure init;
var i:longint;
begin
  fillchar(graph,sizeof(graph),0);
  readln(n,e);
  for i:=1 to e do
   begin
     readln(u,v);
     graph[u,v]:=1;
     graph[v,u]:=1;
   end;
end;
begin
  fillchar(vis,sizeof(vis),0);
  init;
  k:=0;
  bfs;
end.