我们完全可以在书的数量大于5时，直接除于5，得到余数，当数目可以变为x*5+2*4时，则购入X套与2套4本，这是极好的。。。。

1 #include 
    
      2 using namespace std; 3  4 void main() 5 { 6     int x; 7     cout << "请输入要购买的本数：" << endl;  8     cin >> x; 9 10     int i;11     i = x/5;12 13     if (x < 5)14     {15         switch(x)16         {17         case 1:18             cout << "买1本书最低价格为8元"<< endl;19             break;20         case 2:21             cout << "买2本书最低价格为" << x*8*0.95 << "元"<< endl;22             break;23         case 3:24             cout << "买3本书最低价格为" << x*8*0.9 << "元"<< endl;25             break;26         case 4:27             cout << "买4本书最低价格为" << x*8*0.8 << "元"<< endl;28         }29     }30     else{31         switch(x%5)32         {33         case 0:34             cout << "买" << i << "套5本的" << endl;35             cout << "最低价格为：" << i*8*5*0.75<< endl;36             break;37         case 1:38             cout << "买" << i << "套5本的" << endl;39             cout << "外加" << x%5 << "本" << endl;40             cout << "最低价格为：" << i*8*5*0.75 + (x%5)*8<< endl;41             break;42         case 2:43             cout << "买" << i << "套5本的" << endl;44             cout << "外加" << x%5 << "本" << endl;45             cout << "最低价格为：" << i*8*5*0.75 + (x%5)*8*0.95 << endl;46             break;47         case 3://特殊情况48             cout << "买" << i-1 << "套5本的" << endl;49             cout << "外加2套4本" << endl;50             cout << "最低价格为：" << (i-1)*8*5*0.75 + 2*4*8*0.8 << endl;51             break;52         case 4:53             cout << "买" << i << "套5本的" << endl;54             cout << "外加" << x%5 << "本" << endl;55             cout << "最低价格为：" << i*8*5*0.75 + (x%5)*8*0.8 << endl;56         }57     }58 }