[C++ Primer Plus] 第5章、循环和关系表达式（一）程序清单——指针自加减优先级

程序5.4

 #include<iostream>
 using namespace std;

 const int Size = ;

 void main() {
     long long factorials[Size];
     factorials[] = factorials[] = 1LL;
     for (int i = ; i < Size; i++)
     {
         factorials[i] = i*factorials[i - ];
     }
     for (int i = ; i < Size; i++)
     {
         cout << i << "!=" << factorials[i] << endl;
     }
     system("pause");
 }

factorials阶乘函数

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递增/递减运算符和指针

前缀递增递减和*优先级相同，从右到左；

后缀递增递减比前缀优先级高，从左到右。

比如

int arr[] = { ,,,, };
int *p = arr;

*++p：p先自＋，然后*p，最终为3

++*p：先*，然后再++，最终为2

*p++：值为arr[0],即1，该语句执行完毕后，p指向arr[1]（因为后缀优先级高，所以等价于*(p++)，自增p并返回自增之前指向的值）

程序5.8

 #include<iostream>
 using namespace std;

 void main() {
     double sum = 0.0, number;
     cout << "The Amazing Accounto will sum and average five numbers for you.." << endl;
     cout << "Please enter five values: " << endl;
     for (int i = ; i < ; i++)
     {
         cout << "Value " << i << ":";
         cin >> number;
         sum += number;
     }
     cout << "Sum=" << sum << endl;
     cout << "Average=" << sum/ << endl;

     system("pause");
 }

程序5.9（反转字符串）

 #include<iostream>
 #include<string>
 using namespace std;

 void main() {
     cout << "Enter a word:";
     string word;
     cin >> word;
     char tmp;//tmp也可以在循环体内部定义，这样的话将在每次循环中都分配和释放，效率稍微慢一点
     for (int j = ,i=word.size()-; j < i; ++j,--i)//word.size()不包括‘\0’，前缀递增递减在某些情况下比后缀递增递减效率更高
     {
         tmp = word[i];
         word[i] = word[j];
         word[j] = tmp;
     }
     cout << word << endl;

     system("pause");
 }

程序5.14（延时等待）

 #include<iostream>
 #include<ctime>
 using namespace std;

 void main() {
     cout << "Enter the delay time,in seconds:";
     float sec;
     cin >> sec;
     clock_t delay = sec*CLOCKS_PER_SEC;//CLOCKS_PER_SEC每秒钟包含的系统时间单位数。    秒数*CLOCKS_PER_SEC=系统时间
     cout <<"starting\a"<< endl;
     clock_t start = clock();
     while (clock() - start < delay)//当不满足条件时跳出循环
         ;
     cout << "done\a\n";
     system("pause");
 }

当starting显示的时候会响一声，done出现的时候再响一声，中间的时间间隔取决于输入的数字。

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类型别名

程序5.16（cin）

#include<iostream>
using namespace std;

void main() {
    cout << "Enter characters(enter # to quit):" << endl;
    char ch;
    int count = ;
    cin >> ch;
    while (ch != '#')
    {
        cout << ch;
        ++count;
        cin >> ch;
    }
    cout << endl << count << " characters read\n";
    system("pause");
}

可以注意到：1.没有空格和换行符；2.输入#之后还能继续输入

这是因为cin在读取char值时，将忽略空格和换行符；另外，发送给cin的输入被缓冲，这意味着只有在按下回车后，输入的内容才会发送给程序。

程序5.17+5.18+5.19(cin.get和EOF)

程序5.20

 #include<iostream>
 using namespace std;

 const int City = ;
 const int Year = ;

 void main() {
     const char *city[City] = {
         "Gribble City ",
         "Gribbletown",
         "New Gribble ",
         "San Gribble ",
         "Gribble Vista"
     };
     int maxtemps[Year][City] =
     {
         {,,,,},
         {,,,, },
         {,,,,},
         {,,,,}
     };
     cout << "Maxinum temperatures for 2008~2011" << endl;
     for (int i = ; i < City; i++)
     {
         cout << city[i] << ":\t";
         for (int year = ; year < Year; year++)
             cout << maxtemps[year][i] << "\t";
         cout << endl;
     }
     system("pause");
 }