第五章循环和关系表达式

cin.get(ch)调用将一个值放在 ch 中，因为改变了值，<br>在C语言中，改变变量的值，必须将变量的地址传递给<br>函数。但是这个传递的不是&amp;ch，而是ch，这样子在C++<br>上是有效的，只要函数将参数声明为引用类型。<br>//怎么声明为引用类型？？？

<div>i am a student</div><div>i am a student &nbsp;&nbsp;</div><div>you are a teacher</div><div>you are a teacher</div><div>^Z</div><div>33</div>

说明

cin.get(ch);<br>while ( cin.fail() == false )<br>{<br>&nbsp; &nbsp; &nbsp;.....<br>&nbsp; &nbsp; cin.get(ch);<br>}

while ( &nbsp;!cin.fail() &nbsp;)

while ( ！cin.eof() )

cin.get(ch);<br>while ( cin )<br>{<br>&nbsp; &nbsp; &nbsp;.....<br>&nbsp; &nbsp; cin.get(ch);<br>}

原因

意义

<br>while (&nbsp;cin.get(ch))<br>{<br>&nbsp; &nbsp;....<br>}

说明

原理

char ch;<br>cin.get(ch);<br>while ( ch != EOF )<br>{<br>&nbsp; &nbsp; &nbsp;.....<br>&nbsp; &nbsp; cin.get(ch);<br>} //不标准，看下cin.get()如何处理EOF

//正确<br>int ch;<br>ch = cin.get(); //键盘中输入字符，就算ch为char 型，返回的值也是整数<br>while ( ch != EOF)<br>{<br>&nbsp; &nbsp; &nbsp;.....<br>&nbsp; &nbsp; &nbsp;ch = cin.get();<br>}&nbsp;

可使用cin 和eof(),fail() 判断输入是否成功

子主题

返回值

参数

cin.get()如何处理EOF&nbsp;

返回值

参数

返回值

参数

不能处理EOF&nbsp;

<span style="font-family: Arial; font-size: 14px; line-height: 26px; color: rgb(255, 0, 0);">cin.get()和cin.get(ch)之间的区别：</span><br style="color: rgb(54, 46, 43); font-family: Arial; font-size: 14px; line-height: 26px;"><span style="font-family: Arial; font-size: 14px; line-height: 26px; color: rgb(0, 0, 153);">属性 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; cin.get(ch) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ch=cin.get()<br>传递输入字符的方式&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 赋给参数ch &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 将返回值赋给ch<br>用于字符输入时函数返回值 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; istream类对象（执行bool转换后为true）&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; int类型的字符编码<br>到达EOF时函数的返回值 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;istream类对象（执行bool转换后为false） &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 符号常量EOF</span>

使用选择

参数

参数

C++11不在用循序点这个概念

递增表达式的值没有被使用，使用效果是相同的（x++，++x）

前缀，后缀对执行速度有差别。<br>内置类型——没什么区别：<br>类（用户定义的类型）——前缀比后缀版本效率高

前缀运算符和解除引用运算符的优先级相同，结合从右→左

后缀运算符比前缀运算符的优先级高

*++pt

++*pt

(*pt)++

*pt++

c-风格字符串不可以

比较

= for(int i=0 ; i&lt;N ; i++)<br>&nbsp; &nbsp;{<br>&nbsp; &nbsp; &nbsp; &nbsp;double x=prices[i];<br>&nbsp; &nbsp; &nbsp; &nbsp;std::cout &lt;&lt; x ;&nbsp;<br>&nbsp; &nbsp;}

while( str[i] ) &nbsp;= while (str[i] != '\0')

<div>int i=0;</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>string str1 , str2;</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>str1="ancd";</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>while (str1[i] !='\0')</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>{</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>cout&lt;&lt;str1[i];</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>i++;</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>}</div>

疑问：string 类对象不使用空字符来标记字符串末尾，那为什么<br>还可以这样？？？

for

返回程序开始执行后所用的系统时间

time.h

系统时间（clock（）)/ CLOCKS_PER_SEC

秒数（日常生活中的秒数）* CLOCK_PER_SEC

clock_t 为clock 返回类型的别名，所以可以声明 clock_t 类型的变量

子主题

#define BYTE char

问题

typedef char byte;