无符号数的识别

1、无符号数的词法分析程序一、实验目的和要求（1）初步掌握编译原理的实验的技能；（2）验证所学理论、巩固所学知识并加深理解。二、实验内容和原理内容：掌握词法分析的基本思想，并用高级语言编写无符号数（包括整数和实数）的词法分析程序。要求：从键盘中输入一字符串（包括字母、数字等），编写程序识别出其中的无符号数。无符号数的文法规则课定义如下： <无符号数> <无符号实数>|<无符号整数> <无符号实数> <无符号整数>.<数字串>E<比例因子> <比例因子> <有符号整数> <有符号整数&g

2、t; +|-<无符号整数> <无符号整数> <数字串> <数字串> <数字><数字> <数字> 0 1 2 3 4 5 6 7 8 9 本实验中我利用了状态转化图的思想，下面是试验中用到构造的状态转化图：描述状态机的代码格式如下：int state = S0 ;while(1)Switch(state)case S0 : 推荐精选if(T0转移条件满足) 状态转移到满足T0的次态；操作；if(T1转移条件满足) 状态转移到满足T1的次态；操作；if(T2转移条件满足) 状态转移到满足T2的次态；操作；Break

3、 ; case S1 : /插入S1状态下的操作； break ； 实验代码：/本程序主要实现实数的识别import java.io.BufferedReader ;import java.io.IOException ;import java.io.InputStreamReader ;public class RealNumberIdentified /*-成员变量的定义-*/private final int S_0 = 0 ; private final int S_1 = 1 ; private final int S_2 = 2 ; private final int S_3 =

4、3 ; private final int S_4 = 4 ; private final int S_5 = 5 ; private final int S_6 = 6 ; private final int S_7 = 7 ; private char originNumber ; /用来记录原始的数字串 private String resultNumber = new String( ) ; private int realnumberAmount = 0 ; /用来记录识别出的实数的个数 private int realnumberFlag = 0 ; /用于标识该实数是正数还是负数

5、 private int eFlag = 0 ; /用来标识该实数是不是指数实数 private int pointFlag = 0 ; /用来标识该实数是否是小数推荐精选 private int basePlusMinus = 1 ; /用来标识底数的符号 private int count = 0 ; /用来记录已经识别数字串的位数 private int currentState = S_0 ; /用来记录当前所处于的状态 /*- -*/ /*-该方法用来初始化一些参数-*/ private void init( ) resultNumber = new String( ) ; base

6、PlusMinus = 1 ; eFlag = 0 ; pointFlag = 0 ; /*-*/ /*-init( )方法用于去除实数串开始和结尾的无效的空格-*/ private void initOriginNumber( String str ) str = str.trim( ) ; str += '#' ; originNumber = str.toCharArray( ) ; /*-*/ /*-printResult()方法用来输出识别的结果-*/ private void printResult( ) if( realnumberFlag = 0 ) Syste

7、m.out.println( "n识别结束，您所输入的字符串中不包含任何实数！" ) ; else realnumberAmount + ; if( realnumberAmount = 1 ) System.out.println( "n识别结束，您所输入的字符串中所包含的实数如下：" ) ; if( resultNumber.length( ) != 0 )推荐精选 if( eFlag = 1 ) if( basePlusMinus = 1 ) System.out.println( "正指数实数：" + Double.parse

8、Double( resultNumber ) ) ; else System.out.println( "负指数实数：" + Double.parseDouble( resultNumber ) ) ; else if( pointFlag = 1 ) System.out.println( " 小 数 ：" + Double.parseDouble( resultNumber ) ) ; else if( basePlusMinus = 1 ) System.out.println( " 正 整 数：" + Long.parseLo

9、ng( resultNumber ) ) ; else System.out.println( " 负 整 数：" + Long.parseLong( resultNumber ) ) ; /*-*/ /*-识别该实数串的过程-*/ private void identifiedProcess( String str ) initOriginNumber( str ) ; while( count < originNumber.length ) switch( currentState ) case S_0 : if( originNumber count = 

10、9;+' ) resultNumber = resultNumber + originNumber count ; currentState = S_1 ; 推荐精选 else if( originNumber count = '-' ) resultNumber = resultNumber + originNumber count ;basePlusMinus = 0 ;currentState = S_1 ;else if( originNumber count >=48 && originNumber count <=57 )resu

11、ltNumber = resultNumber + originNumber count ; realnumberFlag = 1 ;currentState = S_2 ;else currentState = S_0 ; count + ; break ; case S_1 : if( originNumber count >=48 && originNumber count <=57 ) resultNumber = resultNumber + originNumber count ; realnumberFlag = 1 ; currentState =

12、S_2 ; else resultNumber = resultNumber.substring( 0 , resultNumber.length( ) - 1 ) ;currentState = S_0 ; count + ; break ;推荐精选 case S_2 : if( originNumber count = '.' ) resultNumber = resultNumber + originNumber count ;currentState = S_3 ; else if( originNumber count >=48 && origi

13、nNumber count <=57 ) resultNumber = resultNumber + originNumber count ;currentState = S_2 ; else if( originNumber count = 'E' | originNumber count = 'e' ) resultNumber = resultNumber + originNumber count ;currentState = S_5 ; else if( originNumber count = '+' | originNumbe

14、r count = '-' )count - ;printResult( ) ;init( ) ;currentState = S_0 ; count + ; break ; case S_3 : if( originNumber count >=48 && originNumber count <=57 ) resultNumber = resultNumber + originNumber count ; pointFlag = 1 ;推荐精选currentState = S_4 ; else resultNumber = resultNumbe

15、r.substring( 0 , resultNumber.length( ) - 1 ) ; printResult( ) ; init( ) ; currentState = S_0 ; count + ; break ; case S_4 : if( originNumber count >=48 && originNumber count <=57 ) resultNumber = resultNumber + originNumber count ;currentState = S_4 ; else if( originNumber count = 

16、9;E' | originNumber count = 'e' )resultNumber = resultNumber + originNumber count ;currentState = S_5 ;else if( originNumber count = '+' | originNumber count = '-' )count - ;printResult( ) ;init( ) ;currentState = S_0 ; count + ; break ; 推荐精选 case S_5 : if( originNumber c

17、ount = '+' ) resultNumber = resultNumber + originNumber count ; currentState = S_6 ; else if( originNumber count = '-' ) resultNumber = resultNumber + originNumber count ;currentState = S_6 ;elseif( originNumber count >= 49 && originNumber count <= 57 )resultNumber = re

18、sultNumber + originNumber count ;eFlag = 1 ;currentState = S_7 ;elseresultNumber = resultNumber.substring( 0 , resultNumber.length( ) - 1 ) ; printResult( ) ; init( ) ; currentState = S_0 ; count - ; count + ; break ; case S_6 : if( originNumber count >= 49 && originNumber count <= 57

19、) resultNumber = resultNumber + originNumber count ; eFlag = 1 ;推荐精选currentState = S_7 ; else resultNumber = resultNumber.substring( 0 , resultNumber.length( ) - 2 ) ; printResult( ) ; init( ) ; currentState = S_0 ; count -= 2 ; count + ; break ; case S_7 : if( originNumber count >= 48 && originNumber count <= 57 ) resultNumber = resultNumber + originNumber count ;currentState = S_7 ; else if( originNumber count = '+' | originNumber count = '-&