说明：  该函数是词法分析程序的核心,它可以识别出源程序中的编写错误,以及找出关键字,变量等.具体请看源代码，注释很详细，但是肯定有不足的地方，请大家不吝赐教.
(Lexical Analysis of the function is the core of the procedure, which can identify the source of the preparation of an error, and to identify keywords and other variables. For details, please read the source code, comments, very detailed, but it is certainly inadequate, please everyone wing .)