[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 = 16;

void main() {
    long long factorials[Size];
    factorials[1] = factorials[0] = 1LL;
    for (int i = 2; i < Size; i++)
    {
        factorials[i] = i*factorials[i - 1];
    }
    for (int i = 0; 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[5] = { 1,3,5,7,9 };
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 = 1; i < 6; i++)
    {
        cout << "Value " << i << ":";
        cin >> number;
        sum += number;
    }
    cout << "Sum=" << sum << endl;
    cout << "Average=" << sum/5 << 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 = 0,i=word.size()-1; j < i; ++j,--i)//word.size()不包括‘’，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 <<"startinga"<< endl;
    clock_t start = clock();
    while (clock() - start < delay)//当不满足条件时跳出循环
        ;
    cout << "donea
";
    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。

---

 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 = 0;
    cin >> ch;
    while (ch != '#')
    {
        cout << ch;
        ++count;
        cin >> ch;
    }
    cout << endl << count << " characters read
";
    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 = 5;
const int Year = 4;

void main() {
    const char *city[City] = {
        "Gribble City ",
        "Gribbletown",
        "New Gribble ",
        "San Gribble ",
        "Gribble Vista"
    };
    int maxtemps[Year][City] =
    {
        {96,100,87,101,105},
        {96,98,91,107,104 },
        {97,101,93,108,107},
        {98,103,95,109,108}
    };
    cout << "Maxinum temperatures for 2008~2011" << endl;
    for (int i = 0; i < City; i++)
    {
        cout << city[i] << ":	";
        for (int year = 0; year < Year; year++)
            cout << maxtemps[year][i] << "	";
        cout << endl;
    }
    system("pause");
}