文件名称:wordanalysis
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、该个词法分析器要求至少能够识别以下几类单词：
a． 关键字：else if int return void while共6个，所有的关键字都是保留字，并且必须是小写；
b． 标识符：识别与C语言词法规定相一致的标识符，通过下列正则表达式定义：ID = letter (letter | digit)*；
c． 常数：NUM=(+ | - |ε)digit digit*(.digit digit* |ε)(e(+ | - |ε) digit digit* |ε)，letter = a|..|z|A|..|Z|，digit = 0|..|9，包括整数，如123, -123, +123等；小数，如123.45, +123.45, -123.45；科学计数法表示的常数，如+1.23e3，-2.3e-9；
d． 专用符号：+ - * / < <= > >= == != = , ( ) [ ] { } /* */；
-, Which require at least a lexical analyzer can identify the following types of words: a. Keyword: else if int return void while a total of six, all keywords are reserved words and must be lowercase b. Identifier: Identification and C language provides consistent lexical identifiers, through the definition of the following regular expression: ID = letter (letter | digit)* c. Constants: NUM = (+ |- | Ε) digit digit* (. Digit digit* | ε) (e (+ |- | Ε) digit digit* | ε), letter = a | .. | z | A | .. | Z |, digit = 0 | .. | 9, including integer, such as 123,-123,+ 123, etc. decimals, such as 123.45,+ 123.45,-123.45 science express constant counting method, such as+ 1.23e3,-2.3e-9 d. Special symbols:+-*/
a． 关键字：else if int return void while共6个，所有的关键字都是保留字，并且必须是小写；
b． 标识符：识别与C语言词法规定相一致的标识符，通过下列正则表达式定义：ID = letter (letter | digit)*；
c． 常数：NUM=(+ | - |ε)digit digit*(.digit digit* |ε)(e(+ | - |ε) digit digit* |ε)，letter = a|..|z|A|..|Z|，digit = 0|..|9，包括整数，如123, -123, +123等；小数，如123.45, +123.45, -123.45；科学计数法表示的常数，如+1.23e3，-2.3e-9；
d． 专用符号：+ - * / < <= > >= == != = , ( ) [ ] { } /* */；
-, Which require at least a lexical analyzer can identify the following types of words: a. Keyword: else if int return void while a total of six, all keywords are reserved words and must be lowercase b. Identifier: Identification and C language provides consistent lexical identifiers, through the definition of the following regular expression: ID = letter (letter | digit)* c. Constants: NUM = (+ |- | Ε) digit digit* (. Digit digit* | ε) (e (+ |- | Ε) digit digit* | ε), letter = a | .. | z | A | .. | Z |, digit = 0 | .. | 9, including integer, such as 123,-123,+ 123, etc. decimals, such as 123.45,+ 123.45,-123.45 science express constant counting method, such as+ 1.23e3,-2.3e-9 d. Special symbols:+-*/
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wordanalysis.txt