求教下

#include <iostream>

using namespace std;



int main() {

  char ch1 = 0, ch2 = 0, ch3 = 0, ch4 = 0;

  cout << "Enter four characters: ";

  cin >> ch1 >> ch2 >> ch3 >> ch4;



  unsigned int packed = ch1;

  packed = (((((packed << 8) | ch2) << 8) | ch3) << 8) | ch4;

  cout << "Value of packed characters: "  //这里的两行看不懂是什么意思..

    << std::hex << std::showbase << packed << endl;



  unsigned int mask = 0xff;  

  ch1 = packed & mask;

  ch2 = packed >> 8 & mask;

  ch3 = packed >> 16 & mask;

  ch4 = packed >> 24 & mask;

  cout << "Characters in reverse order are: "  //题目意思明白，但是程序不懂..请懂的指教下.

       << ch1 << ch2 << ch3 << ch4 << endl;;

  return 0;



}