lx.txt

设计目的 加深对语法分析程序的任务及其工作原理的理解；掌握语法分析程序的实现方法；掌握简单语言的状态转换图表示形式极其识别程序的构造。 设计任务 编写对简单语言进行语法分析的词法分析程序。并对输入串f

#include "stdio.h"
#include "ctype.h"
#include "math.h"
#include  "iostream.h"
#include"string.h"
#define LETTER  0
#define DIGIT   1
#define POINT   2
#define OTHER    3
#define POWER   4
#define PLUS    5
#define MINUS    6
#define ClassNo   100
#define ClassOther   200
#define EndState   -1
char num[100];
int w,n,p,e,d;
int Class,i=0;
int ICON;
float FCON;
static int CurrentState;

int GetChar(void);
int EXCUTE(int,int);
int LEX(void);

int HandleOtherWord(void)
{
    return ClassOther;
}

int HandleError(void)
{
    printf("ERROR!\n");
    return 0;
}

int GetChar(void)
{
    int c;

    c=num[i++];

    if(isdigit(c))
    {
        d=c-'0';return DIGIT;
    }
    if(c=='.')return POINT;
    if(c=='E'||c=='e')return POWER;
    if(c=='+') return PLUS;
    if(c=='-')return MINUS;
    return OTHER;
}
//============================================

int EXCUTE(int state,int symbol)
{
    switch (state)
    {
    case 0:switch(symbol)
           {
            case DIGIT:n=0;p=0;e=1;w=d;CurrentState=1;Class=ClassNo;break;
            case POINT:w=0;n=0;p=0;e=1;CurrentState=3;Class=ClassNo;break;
            default:HandleOtherWord();Class=ClassOther;
                CurrentState=EndState;
           }
        break;
    case 1:switch(symbol)
           {
        case DIGIT:w=w*10+d;break;
        case POINT:CurrentState=2;break;
        case POWER:CurrentState=4;break;
        default:FCON=w;CurrentState=EndState;
           }
        break;
    case 2:switch(symbol)
           {
            case DIGIT:n++;w=w*10+d;break;
            case POWER:CurrentState=4;break;
            default:FCON=w*pow(10,e*p-n);CurrentState=EndState;
           }
        break;
    case 3:switch(symbol)
           {
            case DIGIT:n++;w=w*10+d;CurrentState=2;break;
            default:HandleError();CurrentState=EndState;
           }
        break;
    case 4:switch(symbol)
           {
            case DIGIT:p=p*10+d;CurrentState=6;break;
            case MINUS:e=-1;CurrentState=5;break;
            case PLUS:CurrentState=5;break;
            default:HandleError();CurrentState=EndState;
           }
        break;
    case 5:switch(symbol)
           {
               case DIGIT:p=p*10+d;CurrentState=6;break;
               default:HandleError();CurrentState=EndState;

           }
        break;
    case 6:switch(symbol)
           {
            case DIGIT:p=p*10+d;break;
            default:FCON=w*pow(10,e*p-n);CurrentState=EndState;

           }
        break;

    }
return CurrentState;
}


int LEX(void)
{
    int ch;
    CurrentState=0;
        while(CurrentState!=EndState)        
        {
            ch=GetChar();
            EXCUTE(CurrentState,ch);
        }
        return Class;
}
void main()
{ printf("please input\n");
scanf("%s",num);

LEX();
// cout<<ICON<<endl;
cout<<FCON<<endl;

}