Introduction

1、C语言于1972年发明，首次使用是用于重写UINX操作系统(UNIX以前是用汇编写的)

It has been closely associated with the UNIX system where it was developed, since most of the system and most of the programs that run on it are written in C

2、C语言是面向过程的

3、BCPL—>B—>C

BCPL and B are “typeless” languages. By contrast, C provides a variety of data types.

4、C语言的数据类型有：整型(int)、实型(float)、字符型(char)、数组类型(int [])、指针类型(void *)、结构体类型(struct)、共用体类型(union)等。

fundamental types: characters、integers、floating-point numbers of several sizes
derived data types: pointers、arrays、structures、unions

5、控制流

fundamental control-flow constructions:
(1)statement grouping
(2)decision making：if-else
(3)selecting one of a set of possible cases：switch
(4)looping with the termination test at:1⃣️the top：while/for2⃣️the bottom：do-while
(5)early loop exit：break

6、由于C语言允许直接访问物理地址，可以直接对硬件进行操作，因此它既具有高级语言的功能，又具有低级语言的许多功能，能够像汇编语言一样对位（bit）、字节和地址进行操作，而这三者是计算机最基本的工作单元。

C is a relatively “low level” language