無符號數(shù)的識別

1、無符號數(shù)的詞法分析程序一、實驗目的和要求（1）初步掌握編譯原理的實驗的技能；（2）驗證所學理論、鞏固所學知識并加深理解。二、實驗內容和原理內容：掌握詞法分析的基本思想，并用高級語言編寫無符號數(shù)（包括整數(shù)和實數(shù)）的詞法分析程序。要求：從鍵盤中輸入一字符串（包括字母、數(shù)字等），編寫程序識別出其中的無符號數(shù)。無符號數(shù)的文法規(guī)則課定義如下： <無符號數(shù)> <無符號實數(shù)>|<無符號整數(shù)> <無符號實數(shù)> <無符號整數(shù)>.<數(shù)字串>E<比例因子> <比例因子> <有符號整數(shù)> <有符號整數(shù)&g

2、t; +|-<無符號整數(shù)> <無符號整數(shù)> <數(shù)字串> <數(shù)字串> <數(shù)字><數(shù)字> <數(shù)字> 0 1 2 3 4 5 6 7 8 9 本實驗中我利用了狀態(tài)轉化圖的思想，下面是試驗中用到構造的狀態(tài)轉化圖：描述狀態(tài)機的代碼格式如下：int state = S0 ;while(1)Switch(state)case S0 : if(T0轉移條件滿足) 狀態(tài)轉移到滿足T0的次態(tài)；操作；if(T1轉移條件滿足) 狀態(tài)轉移到滿足T1的次態(tài)；操作；if(T2轉移條件滿足) 狀態(tài)轉移到滿足T2的次態(tài)；操作；Break ; c

3、ase S1 : /插入S1狀態(tài)下的操作； break ； 實驗代碼：/本程序主要實現(xiàn)實數(shù)的識別import java.io.BufferedReader ;import java.io.IOException ;import java.io.InputStreamReader ;public class RealNumberIdentified /*-成員變量的定義-*/private final int S_0 = 0 ; private final int S_1 = 1 ; private final int S_2 = 2 ; private final int S_3 = 3 ;

4、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 ; /用來記錄原始的數(shù)字串 private String resultNumber = new String( ) ; private int realnumberAmount = 0 ; /用來記錄識別出的實數(shù)的個數(shù) private int realnumberFlag = 0 ; /用于標識該實數(shù)是正數(shù)還是負數(shù) pri

5、vate int eFlag = 0 ; /用來標識該實數(shù)是不是指數(shù)實數(shù) private int pointFlag = 0 ; /用來標識該實數(shù)是否是小數(shù) private int basePlusMinus = 1 ; /用來標識底數(shù)的符號 private int count = 0 ; /用來記錄已經識別數(shù)字串的位數(shù) private int currentState = S_0 ; /用來記錄當前所處于的狀態(tài) /*- -*/ /*-該方法用來初始化一些參數(shù)-*/ private void init( ) resultNumber = new String( ) ; basePlusMinu

6、s = 1 ; eFlag = 0 ; pointFlag = 0 ; /*-*/ /*-init( )方法用于去除實數(shù)串開始和結尾的無效的空格-*/ private void initOriginNumber( String str ) str = str.trim( ) ; str += '#' ; originNumber = str.toCharArray( ) ; /*-*/ /*-printResult()方法用來輸出識別的結果-*/ private void printResult( ) if( realnumberFlag = 0 ) System.out.pr

7、intln( "n識別結束，您所輸入的字符串中不包含任何實數(shù)！" ) ; else realnumberAmount + ; if( realnumberAmount = 1 ) System.out.println( "n識別結束，您所輸入的字符串中所包含的實數(shù)如下：" ) ; if( resultNumber.length( ) != 0 ) if( eFlag = 1 ) if( basePlusMinus = 1 ) System.out.println( "正指數(shù)實數(shù)：" + Double.parseDouble( resu

8、ltNumber ) ) ; else System.out.println( "負指數(shù)實數(shù)：" + Double.parseDouble( resultNumber ) ) ; else if( pointFlag = 1 ) System.out.println( " 小 數(shù) ：" + Double.parseDouble( resultNumber ) ) ; else if( basePlusMinus = 1 ) System.out.println( " 正 整 數(shù)：" + Long.parseLong( resultNu

9、mber ) ) ; else System.out.println( " 負 整 數(shù)：" + Long.parseLong( resultNumber ) ) ; /*-*/ /*-識別該實數(shù)串的過程-*/ private void identifiedProcess( String str ) initOriginNumber( str ) ; while( count < originNumber.length ) switch( currentState ) case S_0 : if( originNumber count = '+' ) r

10、esultNumber = resultNumber + originNumber count ; currentState = S_1 ; else if( originNumber count = '-' ) resultNumber = resultNumber + originNumber count ;basePlusMinus = 0 ;currentState = S_1 ;else if( originNumber count >=48 && originNumber count <=57 )resultNumber = result

11、Number + 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 = S_2 ; else result

12、Number = resultNumber.substring( 0 , resultNumber.length( ) - 1 ) ;currentState = S_0 ; count + ; break ; case S_2 : if( originNumber count = '.' ) resultNumber = resultNumber + originNumber count ;currentState = S_3 ; else if( originNumber count >=48 && originNumber count <=57

13、 ) 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 = '+' | originNumber count = '-'

14、 )count - ;printResult( ) ;init( ) ;currentState = S_0 ; count + ; break ; case S_3 : if( originNumber count >=48 && originNumber count <=57 ) resultNumber = resultNumber + originNumber count ; pointFlag = 1 ;currentState = S_4 ; else resultNumber = resultNumber.substring( 0 , resultNu

15、mber.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 = 'E' | originNumber c

16、ount = 'e' )resultNumber = resultNumber + originNumber count ;currentState = S_5 ;else if( originNumber count = '+' | originNumber count = '-' )count - ;printResult( ) ;init( ) ;currentState = S_0 ; count + ; break ; case S_5 : if( originNumber count = '+' ) resultNum

17、ber = 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 = resultNumber + originNumber coun

18、t ;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 ) resultNumber = resultNumber

19、+ originNumber count ; eFlag = 1 ;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 = '+' | o