说明白一点``可以吗？```要不然都不知要做什么````

c语言版的词法分析器

[em1]
首先，我就不介绍Lex的语法规则了，因为在一些书上这些是重点介绍的内容，把Lex的源程序写在下面，然后讲解。
%{
#define NUMBER 257
#define PLUS 258
#define SUB 259
#define CHEN 260
#define DIV 261
#define LKUO 262
#define YKUO 263
#include <stdio.h>
#include <stdlib.h>
extern int  yylval;
%}
number  [0-9]+
%%
{number}    {yylval=atoi(yytext);printf("%s",yytext);return NUMBER;}
"+"            {printf("%s",yytext);return PLUS;}
"-"            {printf("%s",yytext);return SUB;}
"*"            {printf("%s",yytext);return CHEN;}
"/"            {printf("%s",yytext);return DIV;}
"("        {printf("%s",yytext);return  LKUO;}
")"        {printf("%s",yytext);return  YKUO;}
%%

词法分析程序也要别人代劳，自己写是很容易的事情。
如果用其他辅助工具（如lex&yacc或ParGen等）做起来
就更容易了。

多加分就行 ,啊哈哈哈哈


/*cifa fenxi chengxu*/
#include <stdio.h>
#include <ctype.h>
#include <malloc.h>
#include <stdlib.h>
#include <string.h>
#define NULL 0

FILE *fp;
char cbuffer;
char *key[8]={"if","else","for","while","do","return","break","continue"};//保留字
char *border[6]={",",";","{","}","(",")"};      //界符
char *arithmetic[4]={"+","-","*","/"};          //运算符
char *relation[6]={"<","<=","=",">",">=","<>"};  //关系
char *consts[20];
char *label[20];
int constnum=0,labelnum=0;

int search(char searchchar[],int wordtype)
{     int i=0;
     switch (wordtype) {
     case 1:{for (i=0;i<=7;i++)                //查找保留字
          {  if (strcmp(key[i],searchchar)==0)
             return(i+1);
          }
         return(1);break;
            }
       case 2:{for (i=0;i<=5;i++)               //查找界符
          {  if (strcmp(border[i],searchchar)==0)
              { return(i+1);
          }     
              }
           return(1);break;
          }
            case 3:{for (i=0;i<=3;i++)               //查找运算符
          {  if (strcmp(arithmetic[i],searchchar)==0)
              {    return(i+1);
              }
          }
          return(1);break;
          }
       case 4:{for (i=0;i<=5;i++)         //查找关系运算符
          {       if (strcmp(relation[i],searchchar)==0)
              {      return(i+1);
              }
          }
           return(1);break;
          }
       case 5:{for (i=0;i<=constnum;i++)
          {  if (strcmp(consts[i],searchchar)==0)
               {return(i+1);
               }
          }
          consts[i-1]=(char *)malloc(sizeof(searchchar));
          strcpy(consts[i-1],searchchar);
          constnum++;
          return(i);
          }
       case 6:{for (i=0;i<=labelnum;i++)
          {     if (strcmp(label[i],searchchar)==0)
               {    return(i+1);
               }
          }
          label[i-1]=(char *)malloc(sizeof(searchchar));
          strcpy(label[i-1],searchchar);
          labelnum++;
          return(i);
          }
      }
}
char alphaprocess(char buffer)
{     int atype;
      int i=-1;
      char alphatp[20];
      while ((isalpha(buffer))||(isdigit(buffer)))
        { alphatp[++i]=buffer;
         buffer=fgetc(fp);
        }
      alphatp[i+1]='\0';
      if (atype=search(alphatp,1))
     printf("%s (1,%d)\n",alphatp,atype-1);
      else     {      atype=search(alphatp,6);
                 printf("%s (6,%d)\n",alphatp,atype-1);
              }
      return(buffer);
}
char digitprocess(char buffer)
{     int i=-1;
      char digittp[20];
      int dtype;
      while ((isdigit(buffer)))
        {  digittp[++i]=buffer;
           buffer=fgetc(fp);
        }
      digittp[i+1]='\0';
      dtype=search(digittp,5);
      printf("%s (5,%d)\n",digittp,dtype-1);
      return(buffer);
}

char otherprocess(char buffer)
{      int i=-1;
      char othertp[20];
      int otype,otypetp;
      othertp[0]=buffer;
      othertp[1]='\0';
      if (otype=search(othertp,3))
     {      printf("%s (3,%d)\n",othertp,otype-1);
         buffer=fgetc(fp);
         goto out;
     }
      if (otype=search(othertp,4))
          { buffer=fgetc(fp);
          othertp[1]=buffer;
          othertp[2]='\0';
          if (otypetp=search(othertp,4))
         { printf("%s (4,%d)\n",othertp,otypetp-1);
         goto out;
         }
          else
         othertp[1]='\0';
         printf("%s (4,%d)\n",othertp,otype-1);
         goto out;
          }
      if (buffer==':')
          { buffer=fgetc(fp);
          if (buffer=='=')
         printf(":= (2,2)\n");
         buffer=fgetc(fp);
         goto out;
          }
       else
          {     if (otype=search(othertp,2))
         {     printf("%s (2,%d)\n",othertp,otype-1);
         buffer=fgetc(fp);
         goto out;
         }
          }
      if ((buffer!='\n')&&(buffer!=' '))
          printf("%c error,not a word\n",buffer);
      buffer=fgetc(fp);
out:      return(buffer);
}
void main()
{
     int i;
      for (i=0;i<=20;i++)
      {
       label[i]="";
       consts[i]="";
      };
      if ((fp=fopen("example.c","r"))==NULL)
     printf("error");
      else
    {
    cbuffer = fgetc(fp);
    while (cbuffer!=EOF)
     {
      if (isalpha(cbuffer))
         cbuffer=alphaprocess(cbuffer);
      else if (isdigit(cbuffer))
         cbuffer=digitprocess(cbuffer);
      else cbuffer=otherprocess(cbuffer);
      }
     printf("over\n");
     getchar();
     }
}
自己在编一个 名为example.c就行了

我今天第一次进这论坛
怎么很多朋友都在找词法分析器的代码啊?
哈哈

谢谢 这位大哥

谢谢这位大哥

谢也不给点分?吝啬!!!
我这几天才进论坛看看,就想多拿点分.哈哈
对这没兴趣,就不想进了!

看来我的多学点英语了