diff --git a/Chapter2 C与C++/2.1 基础语法.md b/Chapter2 C与C++/2.1 基础语法.md
index 20d4a72..86076c6 100644
--- a/Chapter2 C与C++/2.1 基础语法.md	
+++ b/Chapter2 C与C++/2.1 基础语法.md	
@@ -181,11 +181,50 @@ ashort++;
 ```
 
 # 2.1.7 符号常量
+有时候我们希望用一个符号来代替某个字面常量，这看起来很像一个不允许改变值的变量，我们用 const 关键字来修饰它，使之成为符号常量。例如：
+
+```cpp
+const long cnvar0=666;
+const char cnvar1='C';
+```
+
+一个符号常量只能在定义时被初始化，并且不能够被再次赋值。例如下面做法是错的：
+
+```cpp
+const int cnint = 256;
+cnint++;
+```
 
 # 2.1.8 运算符
 
+c语言运算符主要包括赋值运算、算数运算、逻辑运算、位运算、比较运算等。运算符主要涉及到优先级,结合性y以及前加加和后加加的问题。例如：
+
+```cpp
+int val=5, mask=0b0100;
+printf("val=%d.\n", val++);   // val=5.
+printf("val=%d.\n", ++val);   // val=7.
+
+if(val<=10 && val>=5)
+{
+  printf("True\n");
+}
+
+val &= mask;  // val=4.
+```
+
 # 2.1.9 宏
 
+通过使用宏，可以指导c编译器做一些特别的工作。例如使用define关键字来做一些替代的工作：
+```cpp
+#define BASE_ADDR (0x25)
+#define REG1_OFFSET (0x01)
+#define REG2_OFFSET (0x02)
+
+printf("Register 1 addr=0x%x.\n", BASE_ADDR+REG1_OFFSET);
+printf("Register 2 addr=0x%x.\n", BASE_ADDR+REG2_OFFSET);
+```
+这称作宏替换。宏替换可以提高程序的可移植性，例如上述例子中，只要修改 #define BASE_ADDR (0x25) 一处便可以修改所有寄存器的地址。
+
 # 2.1.10 指针
 
 指针变量的长度与总线位宽有关，如32位机则指针变量长度为4，64位机为8。
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