词法分析器
//此程序读取infile.txt文件的信息进行词法分析，相应分析结果写入到自动生成的outfile.txt文件中
#include <stdio.h>
#include <string.h>
#include <process.h>
#define MAX 50
void main()
{
FILE *in,*out;/*存放输入字符串和输出单词串的文件*/
char arr[MAX];/*arr数组存放单词符号*/
char currentchar;/*currentchar存放当前输入字符*/
int i=0;/*arr数组的一个指针*/
/*以读方式打开输入文件*/
if((in=fopen("infile.txt","r"))==NULL)
{
 printf("can not open file\n");
 exit(0);
}
/*以写方式打开输出文件*/
if((out=fopen("outfile.txt","w"))==NULL)
{
 printf("cannout open outfile\n");
    exit(1);
}
//去掉开头空格
currentchar=fgetc(in);
while(currentchar==' ')
{
 currentchar=fgetc(in);
}
int ch;

while(currentchar!='@')
{
/*常数部分判断*/
if((currentchar>='a'&&currentchar<='z')||(currentchar>='A'&&currentchar<='Z')||(currentchar>='0'&&currentchar<='9')||currentchar=='>'||currentchar=='<'||currentchar==';'||currentchar==':'||currentchar=='+'||currentchar=='-'||currentchar=='*'||currentchar=='/'||currentchar=='='||(ch=currentchar)=='\n'||currentchar==' ')
{
i=0;//清空arr字符数组
if(currentchar>='0'&&currentchar<='9')
{
 arr[i++]=currentchar;
    currentchar=fgetc(in);//再读入下一个字符
    while(currentchar>='0'&&currentchar<='9')
 {
    arr[i++]=currentchar;
    currentchar=fgetc(in);
 }
    if(currentchar!='.')//如果当前读入的符号不为小数点，则常数读完毕，输出此常数
 {
    arr[i++]='\0';
    fprintf(out,"%s%d,%c%s%c%s\n","(",11,'"',arr,'"',")");//格式化输出到目标文件,11代表种别码， arr为内码值，规定用数字本身代表
 }
    else//当前字符为小数点则继续向下读入
 {
    arr[i++]=currentchar;
    currentchar=fgetc(in);
    while(currentchar>='0'&&currentchar<='9')
 {
    arr[i++]=currentchar;
    currentchar=fgetc(in);
 }
    arr[i++]='\0';
    fprintf(out,"%s%d,%c%s%c%s\n","(",11,'"',arr,'"',")");
 }
    while(currentchar==' ')
 {
 currentchar=fgetc(in);
 }
}
/*判断标识符和关键字部分*/
if((currentchar>='a'&&currentchar<='z')||(currentchar>='A'&&currentchar<='Z'))
{
i=0;//清空arr字符数组
    while((currentchar>='a'&&currentchar<='z')||(currentchar>='0'&&currentchar<='9')||(currentchar>='A'&&currentchar<='Z'))
 {
    arr[i++]=currentchar;
    currentchar=fgetc(in);
 }
//把字符数组arr和关键字表比较，判断单词串是关键字还是标识符
    arr[i++]='\0';
    if(strcmp(arr,"begin")==0)
    fprintf(out,"%s%d,%c%s%c%s\n","(",1,'"',arr,'"',")");
    else if(strcmp(arr,"end")==0)
    fprintf(out,"%s%d,%c%s%c%s\n","(",2,'"',arr,'"',")");
 
  
    else if(strcmp(arr,"if")==0)
    fprintf(out,"%s%d,%c%s%c%s\n","(",3,'"',arr,'"',")");

 
    else if(strcmp(arr,"then")==0)
    fprintf(out,"%s%d,%c%s%c%s\n","(",4,'"',arr,'"',")");
   else if(strcmp(arr,"else")==0)
    fprintf(out,"%s%d,%c%s%c%s\n","(",5,'"',arr,'"',")");
    else if(strcmp(arr,"while")==0)
    fprintf(out,"%s%d,%c%s%c%s\n","(",6,'"',arr,'"',")");
    else if(strcmp(arr,"do")==0)
    fprintf(out,"%s%d,%c%s%c%s\n","(",7,'"',arr,'"',")");
 else
 fprintf(out,"%s%d,%c%s%c%s\n","(",10,'"',arr,'"',")");
}
while(currentchar==' ')
{
 currentchar=fgetc(in);
}
//判断标识符包括：+, -, *, /, (, ), {, }, <, >, ;, :, !=, >=, <=, ==, =.
if(currentchar=='+')
{
    fprintf(out,"%s%d,%c%c%c%s\n","(",13,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{
 currentchar=fgetc(in);
}
if(currentchar=='-')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",14,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{
 currentchar=fgetc(in);
}
if(currentchar=='*')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",15,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{
 currentchar=fgetc(in);
}
if(currentchar=='/')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",16,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}

while(currentchar==' ')
{
 currentchar=fgetc(in);
}
if(currentchar=='<')
{
 i=0;
 arr[i++]=currentchar;
 currentchar=fgetc(in);
 if(currentchar=='=')
 {
  arr[i++]=currentchar;
  arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",17,'"',arr,'"',")");
     currentchar=fgetc(in);
 }
 else if(currentchar=='>')
 {
  arr[i++]=currentchar;
  arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",18,'"',arr,'"',")");
     currentchar=fgetc(in);
 }
 else
 { arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",19,'"',arr,'"',")");
    }
}

while(currentchar==' ')
{
 currentchar=fgetc(in);
}
if(currentchar==':')
{
 i=0;
 arr[i++]=currentchar;
 currentchar=fgetc(in);
 if(currentchar=='=')
 {
  arr[i++]=currentchar;
  arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",22,'"',arr,'"',")");
     currentchar=fgetc(in);
 }
 else
 { arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",21,'"',arr,'"',")");
    }
}

while(currentchar==' ')
{
 currentchar=fgetc(in);
}
if(currentchar==';')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",23,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}

while(currentchar==' ')
{
{需要全部代码请联系QQ3249114
 currentchar=fgetc(in);
}
 while(currentchar==' ')
{
 currentchar=fgetc(in);
}
}
else
{
 fprintf(out,"%s,%c%c%c\n","error",'"',currentchar,'"');
    currentchar=fgetc(in);
}

}//结束开头while语句
/*关闭文件退出*/
fclose(in);
fclose(out);
printf("相应的词法分析结果在自动生成的outfile.txt文件中\n");
}
输出结果：
infile:avgfgvf+b;
<=
@

outfile:(10,"avgfgvf")
(13,"+")
(10,"b")
(23,";")
(17,"<=")