I've been playing around with the code, you can just comment out the bits you don't want to run in the main function...

  // buff.s1number();
  // for (int i = 1; i < argc; i++)
  //  buff.s2banner(argv[i]);
  // buff.s3rain(2800, buffer::s3rain_scroll_func_tanh);
  buff.s4conway();
  // buff.s5mandel();

  // Infinite rain
  //buff.s3rain(0, buffer::s3rain_scroll_func_const);