说明：  三、 实验要求 1. 使用 PL/0 语言编写程序，实现输出斐波那契数列前 20 项数值。 2. 从 PL/0 编译程序源码中抽出词法分析部分，构建 PL/0 独立词法分析程序。功能：输入为 PL/0 源程序， 输出为单词符号的序列；对于标识符和无符号整数，显示单词种别和单词自身的值两项内容；对于其他单词符 号，仅显示其单词种别。 3. 使用 AutoFlowchart 画出独立词法分析程序的程序流程图，并分析每部分的功能和特点。
(Iii. Experimental requirements 1. Use PL/0 language to write programs to output the first 20 values of Fibonacci sequence. 2. Extract the part of lexical analysis from PL/0 compiler source code, and build PL/0 independent lexical analysis program. Function: Input as PL/0 source program, Output a sequence of word symbols; For identifiers and unsigned integers, the word class and the value of the word itself are displayed. For other word characters , showing only its word class. 3. Use AutoFlowchart to draw the program flow chart of the independent lexical analysis program and analyze the functions and characteristics of each part.)