text: #include<ctime>
  #include<cstdio>
  #include<cstdlib>
  char t[]="01ab";
  main()
  {
      int i,j;
      srand(time(NULL));
      for(i=0;i<15;i++)
      {
          for(j=1+rand()%30;j--;)
              putchar(t[rand()%4]);
          puts("");
      }
  }
  