1 Why C?

C language gives programmer great control
e.g. 精确到内存单元, 可循环到内存溢出(python 1000次左右即终止)
Produce faster code
C编译的速度优势是明显的
Widely used
有足够多的support library 和 community support, 同样在industry 和 science上都有足够多的应用，即：从功利的角度和踩坑的角度，这门先祖语言都有足够的优势

2 Brief History

C and UNIX share a complex history
C was originally designed for an implement on UNIX on a PDP-11 computer
Dennis Ritchie was the author of C(1971)
In 1973, UNIX was rewritten in C.
B is the predecessor of C, but there is no A.
In 1983, American National Standard Institute(ANSI) clean up and standardise the language.
In 1988, ANSI C published.
Till now, C is the main language for operation systems and compliers.

3 C language basic knowledge

1 basic structure of C

include files

可以是库函数，也可以是自定义库函数

define var value

全局变量，实际上也是只在本file中使用，不是整个project
file间的变量交流，还是靠函数的传参大法
C function，这个基本上学过编程的人有有所了解，关于形参、实参、返回值等知识略。
int main(argc, argv){}
入口函数，如果以int作为入口函数类型，那么一定有返回值，0代表successful executing, 1代表error occurs.
如果用 void，实际上是默认返回0的int的简写。
入口函数参数：
argc: #parameters, parameter指命令行传入的参数
argv: actual parameters, refer 一个 stackoverflow的例子，很简明。