0x 考试内容要求

1. 掌握C++的数据类型
2. 解常量定义
3. 掌握常量的用法
4. 掌握运算符种类以及其优先级和结合性
5. 熟练掌握表达式

1x C++语言的数据类型

C++将数据类型分为三种：

• 基本数据类型
• 构造类型(导出数据类型)
• 自定义类型

1x.1 基本类型

• 逻辑型——bool
  • BOOL布尔型，用0，1来表示逻辑真假
  • 只拥有个值:true、false分别用1、0表示
• 字符型——char
  • 取值范围：ASCII，扩充ASCII
  • 占用一个字节，即8位
  • ASCII中的字符和整数具有对应关系
  • 取值范围：0~255
• 整型——int
  • 16位机，占2个字节；32位机占4个字节
  • 取值范围为：-32768~32767
• 浮点型——float、double
  • 单精度浮点型(float)占4个字节；
  • 双精度浮点型(double)占8个字节；
• 空类型——void
  • 表示取值为空
  • void *p表示指向类型不明确

1x.1.1 基本类型的派生类型

• 基本类型的派生类型是指——基本类型的字长及其取值范围可以放大和缩小，改变后的类型
• 派生类生命符由基本类型关键字面前加上修饰符组成
  • short——缩短字长
  • long——加长字长
  • signed——有符号类型，取值类型包括正负值
  • unsigned——无符号类型，取值范围只包括正值

    Tip:该规则并不可以应用于全部基本类型具体请参照下表，图片来源：见水印

    

1x.1.2 常量

常量是指在程序执行过程中值不改变的量。

有两种表示形式：字面常量和符号常量。

字面常量

1. 逻辑常量
   • 有两个值：True、False
   • 分别用1、0表示
   • 可以参与算数运算
2. 字符常量
   • 简称字符：以单引号作为起止符号
   • ASCII是字符范围落在字符型类型的范围内，所以也是字符常量（个别字符除外）
   • 转义字符：用反斜杠“\”引导的下一个字符，失去了原来的含义，而转义成了别的意义
   • 允许反斜杠一道一个具有1至3位的八进制数或以x开始标记的1至2位十六进制
3. 整型常量
   • 十进制整数：整数和负数-2³¹~2^31-1
   • 八进制整数：以数字0开头，全部默认为正数
   • 十六进制整数：以数字0和字母x或X开头
   • 整型数表示允许后面添加后缀u或U来表示无符号和l或L来表示长整型
4. 实型常量
   • 定点表示：用小数形式表示实数，小数点可以出在任何一个数字为的前面或者后面

     甚至.01 -.012都是合法的

   • 浮点表示：以指数形式表示
     • 由一个十进制整数后接一个字母E或e和一个1~3位的十进制整数组成，E/e前面的称为尾数，E/e后面的称为指数。
     • 该浮点数的值等于尾数乘以是的指数幂
5. 枚举常量
   • 枚举属于用户定义类型，用enum表示
   • 用来定义程序中的需要使用的一组相关符号常量
   • 声明枚举类型的语法格式

       enum <类型名>{<枚举值1>,<枚举值2>...}；
       //这里的枚举具有顺序性
   

   • 说明
     • 一个枚举类型是int类型的一个子集，每一个枚举值代表着一个整数(默认从0开始，依次加一以表示枚举值的顺序性)
     • 若第i个枚举值常量值为m，则后续的枚举值分别与m+1 m+2对应向前对应为m-1

符号常量

• 由用户定义，定义方法有两种，一种为预编译器的#defined或使用conts关键字。

1x.1.3 变量

• 变量是程序中用于存储信息的单元，它对应于内存中的某段存储空间。
• 定义变量需要说明变量的数据类型和名字
• 数据类型说明为变量分配多少的内存空间
• 变量名可以代表存储空间，因此程序能在变量中存储值和取出值

1. 变量的定义
   1. 定义的格式：

      储存类 变量类型 变量名=初始化值/初始表达式；

      • 默认储存内类为auto
      • 若未赋初值，则变量的值不确定
      • 可以定义多个变量，各个变量之间用逗号运算符,分开
   2. 变量名的命名规则：
      • 必须是一个合法的C++标识符
      • 不能使用C++关键字
2. 变量的使用方法
   1. 全局变量和局部变量
      • 全局变量——在所有函数定义、类定义和程序块之外声明的变量
      • 若没有初始化，系统会自动为其赋值为0

        (这里就和局部变量的自动初始化区别开来)

      • 在程序的任何一个函数、类或者程序块之外都能访问全局变量
      • 局部变量——在某个函数定义、类定义和程序块之类声明的变量
      • 局部变量只能在声明它的局部范围内被访问
   2. 生存期和作用域
      • 生存期——指从一个变量被声明且分配内存开始，直到该变量声明语句失效，它占用的内存空间被释放为止
        • 全局变量——从声明开始，知道程序结束为止
        • 局部变量——从声明开始，到包含它的最近的一个程序块结束为止
      • 作用域——指变量名可以代表该变量储存空间的范围
      • 一般来说，变量的作用域与其声明周期是一致的

        可以使用动态分配空间的方法来控制变量的声明周期

   3. 变量的存储类属性

      C++根据存储方式的不同将存储类别划分为4类:

      • auto变量——自动变量，为变量声明时的默认储存类别
      • register变量——寄存器变量，建议编译器以寄存器作为存储空间
      • static变量——静态变量，声明周期延续到程序的总之，默认赋初始值为0；
      • extern变量——外部变量，通常用于多个文件组成的程序中，多个文件同时被声明指向同一个变量。
   4. typedef类型说明

      使用关键字typedef可以为已有类型名定义一个新类型名，为了提高代码的可读性。

      其格式为：

      typedef [已有类型名] [新类型名]
      

   5. 符号常量声明语句
      • 声明语句格式：

          const [类型名] [符号常量名] = 初值表达式
      

      • 必须在声明符号常量的同事为其赋初值
      • 符号常量的值为常量，以后这个值始终保持不变。不能再次赋值
      • 若类型名为int则可以省略类型名
      • 适当使用可以提高的程序的可读性和可维护性

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.markdown-preview.markdown-preview button { display: inline-block; padding: 4px 14px; font-family: "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 13px; line-height: 18px; background-color: #0064cd; background-repeat: repeat-x; background-image: linear-gradient(top, #049cdb, #0064cd); color: #fff; border: 1px solid #004b9a; border-bottom-color: #003f81; border-color: rgba(0, 0, 0, 0.1) rgba(0, 0, 0, 0.1) rgba(0, 0, 0, 0.25) }
.markdown-preview.markdown-preview button:hover { color: #fff; background-position: 0 -15px; text-decoration: none }
.markdown-preview.markdown-preview button:active { }
.markdown-preview.markdown-preview button::-moz-focus-inner { padding: 0; border: 0 }
.markdown-preview.markdown-preview table { border-spacing: 0; width: 100% }
.markdown-preview.markdown-preview table { border: solid #ccc 1px }
.markdown-preview.markdown-preview table tr:hover { background: #fbf8e9 }
.markdown-preview.markdown-preview table td,.markdown-preview.markdown-preview .table th { border-left: 1px solid #ccc; border-top: 1px solid #ccc; padding: 10px; text-align: left }
.markdown-preview.markdown-preview table th { background-color: #dce9f9; background-image: linear-gradient(top, #ebf3fc, #dce9f9); border-top: none; padding: 5px }
.markdown-preview.markdown-preview table td:first-child,.markdown-preview.markdown-preview table th:first-child { border-left: none }
.markdown-preview.markdown-preview table th:first-child { }
.markdown-preview.markdown-preview table th:last-child { }
.markdown-preview.markdown-preview table th:only-child { }
.markdown-preview.markdown-preview table tr:last-child td:first-child { }
.markdown-preview.markdown-preview table tr:last-child td:last-child { }

原文地址：https://www.cnblogs.com/Earl-Jones/p/8570729.html