无符号数的识别

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[+|-]无符号整数无符号整数数字串数字串数字{数字}数字0123456789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：S1S2S3S4S5S7S6S0+/-数字数字.E/eE/e数字+/-数字数字数字数字数字描述状态机的代码格式如下：intstate=S0;while(1){Switch(state){caseS0: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;caseS1://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importjava.io.BufferedReader;importjava.io.IOException;importjava.io.InputStreamReader;publicclassRealNumberIdentified{/*---------------------------------成员变量的定义---------------------------------------*/privatefinalintS_0=0;privatefinalintS_1=1;privatefinalintS_2=2;privatefinalintS_3=3;privatefinalintS_4=4;privatefinalintS_5=5;privatefinalintS_6=6;privatefinalintS_7=7;privatecharoriginNumber[];//用来记录原始的数字串privateStringresultNumber=newString();privateintrealnumberAmount=0;//用来记录识别出的实数的个数privateintrealnumberFlag=0;//用于标识该实数是正数还是负数privateinteFlag=0;//用来标识该实数是不是指数实数privateintpointFlag=0;//用来标识该实数是否是小数privateintbasePlusMinus=1;//用来标识底数的符号privateintcount=0;//用来记录已经识别数字串的位数privateintcurrentState=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------------------------------------*/privatevoidinit(){resultNumber=newString();basePlusMinus=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----------------*/privatevoidinitOriginNumber(Stringstr){str=str.trim();str+='#';originNumber=str.toCharArray();}/*-----------------------------------------------------------------------------------------*//*---------------------------printResult()方法用来输出识别的结果------------------------*/privatevoidprintResult(){if(realnumberFlag==0)System.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){if(eFlag==1)if(basePlusMinus==1)System.out.println(正指数实数：+Double.parseDouble(resultNumber));elseSystem.out.println(负指数实数：+Double.parseDouble(resultNumber));elseif(pointFlag==1)System.out.println(小数：+Double.parseDouble(resultNumber));else{if(basePlusMinus==1)System.out.println(正整数：+Long.parseLong(resultNumber));elseSystem.out.println(负整数：+Long.parseLong(resultNumber));}}}}/*-----------------------------------------------------------------------------------------*//*--------------------------------识别该实数串的过程-------------------------------------*/privatevoididentifiedProcess(Stringstr){initOriginNumber(str);while(countoriginNumber.length){switch(currentState){caseS_0:{if(originNumber[count]=='+'){resultNumber=resultNumber+originNumber[count];currentState=S_1;}else{if(originNumber[count]=='-'){resultNumber=resultNumber+originNumber[count];basePlusMinus=0;currentState=S_1;}elseif(originNumber[count]=48&&originNumber[count]=57){resultNumber=resultNumber+originNumber[count];realnumberFlag=1;currentState=S_2;}else{currentState=S_0;}}count++;break;}caseS_1:{if(originNumber[count]=48&&originNumber[count]=57){resultNumber=resultNumber+originNumber[count];realnumberFlag=1;currentState=S_2;}else{resultNumber=resultNumber.substring(0,resultNumber.length()-1);currentState=S_0;}count++;break;}caseS_2:{if(originNumber[count]=='.'){resultNumber=resultNumber+originNumber[count];currentState=S_3;}elseif(originNumber[count]=48&&originNumber[count]=57){resultNumber=resultNumber+originNumber[count];currentState=S_2;}elseif(originNumber[count]=='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;}caseS_3:{if(originNumber[count]=48&&originNumber[count]=57){resultNumber=resultNumber+originNumber[count];pointFlag=1;currentState=S_4;}else{resultNumber=resultNumber.substring(0,resultNumber.length()-1);printResult();init();currentState=S_0;}count++;break;}caseS_4:{if(originNumber[count]=48&&originNumber[count]=57){resultNumber=resultNumber+originNumber[count];currentState=S_4;}else{if(originNumber[count]=='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;}caseS_5:{if(originNumber[count]=='+'){resultNumber=resultNumber+originNumber[count];currentState=S_6;}elseif(originNumber[count]=='-'){resultNumber=resultNumber+originNumber[count];currentState=S_6;}elseif(originNumber[count]=49&&originNumber[count]=57){resultNumber=resultNumber+originNumber[count];eFlag=1;currentState=S_7;}else{resultNumber=resultNumber.substring(0,resultNumber.length()-1);printResult();init();currentStat