wa.cpp

采用VC编程的词法分析器

#include<iostream.h>
#include<stdio.h>
#include<stdlib.h> 
#include<string.h>
int i,j,k,flag,number,status;
/*status which is use to judge the string is keywords or not!*/
char ch;
char words[10] = {" "};
char program[500];
int Scan(char program[])
{
    char *keywords[13] = {"void","main","if","then","break","int",
  "char","float","include","for","while","printf",
  "scanf"};
number = 0;
status   = 0;
j      = 0;
ch     = program[i++];
       /* To handle the lettle space ands tab*/

      /*handle letters*/
if ((ch >= 'a') && (ch <= 'z' ))
{
while ((ch >= 'a') && (ch <= 'z' ))
{
words[j++]=ch;
ch=program[i++];
}
  i--;
  words[j++] = '\0';
       for (k = 0; k < 13; k++)
 if (strcmp (words,keywords[k]) == 0)
switch(k)
{
case 0:{
 flag = 1;
 status = 1;
 break;
}
case 1:{
 flag = 2;
 status = 1;
 break;
}
case 2:{
 flag = 3;
 status = 1;
 break;
}
case 3:{
 flag = 4;
 status = 1;
 break;
}
case 4:{
 flag = 5;
 status = 1;
 break;
}
case 5:{
 flag = 6;
 status = 1;
 break;
       }
case 6:{
 flag = 7;
 status = 1;
 break;
       }
case 7:{
 flag = 8;
 status = 1;
 break;
       }
case 8:{
 flag = 9;
 status = 1;
 break;
       }
case 9:{
 flag = 10;
 status = 1;
 break;
       }
case 10:{
 flag = 11;
 status = 1;
 break;
}
case 11:{
 flag = 12;
 status = 1;
 break;
}
case 12:{
 flag = 13;
 status = 1;
 break;
}
}
   if (status == 0)
   {
      flag = 100;
   }
}//判断输入的是否为字符
/*handle digits*/
else if ((ch >= '0') && (ch <= '9'))
{
number = 0;
while ((ch >= '0' ) && (ch <= '9' ))
{
number = number*10+(ch-'0');
ch     = program[i++];
}
flag = 200;
i--;
}//判断输入的是否为数字
/*opereation and edge handle*/
else switch (ch)
{
case '=':{
   if (ch == '=')
     words[j++] = ch;
     words[j]   = '\0';
     ch         = program[i++];
     if (ch == '=')
     {
    words[j++] = ch;
    words[j]   = '\0';
    flag       = 401;
     }
     else
     {
    i--;
    flag       = 402;
     }
   break;
 }
case'>':{
 if (ch == '>')
       words[j++] = ch;
       words[j]   = '\0';
       ch         = program[i++];
   if (ch == '=')
   {
       words[j++] = ch;
       words[j]   = '\0';
       flag       = 403;
   }
   else
   {
       i--;
       flag       = 404;
   }
  break;
}
case'<':{
     if (ch == '<')
        words[j++] = ch;
        words[j]   = '\0';
        ch         = program[i++];
        if (ch == '=')
{
    words[j++] = ch;
    words[j]   = '\0';
    flag       = 405;
}
        else
{
    i--;
    flag       = 406;
}
    break;
}
case'!':{
    if (ch == '!')
       words[j++] = ch;
       words[j]   = '\0';
       ch         = program[i++];
     if (ch == '=')
     {
       words[j++] = ch;
       words[j]   = '\0';
       flag       = 407;
     }
     else
     {
    i--;
       flag       = 408;
     }
    break;
}
case'+':{
   if (ch == '+')
      words[j++] = ch;
      words[j]   = '\0';
      ch         = program[i++];
     if (ch == '=')
     {
    words[j++] = ch;
    words[j]   = '\0';
    flag       = 409;
     }
     else if (ch == '+')
     {
    words[j++] = ch;
    words[j]   = '\0';
    flag       = 410;
     }
     else
     {
i--;
flag       = 411;
     }
   break;
}
case'-':{
  if (ch == '-')
   words[j++] = ch;
   words[j]   = '\0';
   ch         = program[i++];
   if (ch == '=')
   {
words[j++] = ch;
words[j]   = '\0';
flag       = 412;
   }
   else if( ch == '-')
   {
words[j++] = ch;
words[j]   = '\0';
flag       = 413;
   }
   else
   {
    i--;
flag       = 414;
   }
   break;
}
case'*':{
  if (ch == '*')
      words[j++] = ch;
      words[j]   = '\0';
      ch         = program[i++];
      if (ch == '=')
      {
   words[j++] = ch;
   words[j]   = '\0';
   flag       = 415;
      }
     else
     {
   i--;
   flag       = 416;
     }
   break;
 }
case'/':{
 if (ch == '/')
       words[j++] = ch;
       words[j]   = '\0';
       ch         = program[i++];
       if (ch == '=')
       {
       words[j++] = ch;
       words[j]   = '\0';
       flag       = 417;
       }
       else
       {
       i--;
       flag       = 418;
       }
  break;
}
case';':{
  words[j]   = ch;
  words[j+1] = '\0';
  flag       = 501;
  break;
 }
case'(':{
  words[j]   = ch;
  words[j+1] = '\0';
  flag       = 502;
  break;
 }
case')':{
  words[j]   = ch;
  words[j+1] = '\0';
  flag       = 503;
  break;
}
case'[':{
  words[j]   = ch;
  words[j+1] = '\0';
  flag       = 504;
  break;
 }
case']':{
  words[j]   = ch;
  words[j+1] = '\0';
  flag       = 505;
  break;
 }
case'{':{
  words[j]   = ch;
  words[j+1] = '\0';
  flag       = 506;
  break;
 }
case'}':{
  words[j]   = ch;
  words[j+1] = '\0';
  flag       = 507;
  break;
 }
case':':{
  words[j]   = ch;
  words[j+1] = '\0';
  flag       = 508;
  break;
}
case'"':{
  words[j] = ch;
  words[j+1] = '\0';
  flag = 509;
  break;
}
case'%':{
   if (ch == '%')
       words[j++] = ch;
       words[j]   = '\0';
       ch         = program[i++];
       if (ch == '=')
       {
       words[j++] = ch;
       words[j]   = '\0';
       flag       = 510;
       }
       else
       {
       i--;
       flag       = 511;
       }
     break;
}
case',':{
 words[j] = ch;
 words[j+1] = '\0';
 flag = 512;
 break;
}
case'#':{
 words[j] = ch;
 words[j+1] = '\0';
 flag = 513;
 break;
}
case'.':{
 words[j] = ch;
 words[j+1] = '\0';
 flag = 514;
 break;
}
case'\n':{
 words[j] = ch;
 words[j+1] = '\0';
 flag = 515;
 break;
}
case'@':{
 words[j] = '#';
 flag = 0;
 break;
}

 
default:{
 flag = -1;
 break;
}
}
return flag;
}//判断特殊符号
main()
{
i=0;
printf("please input a program end with @");
do
{
  ch           = getchar();
  program[i++] = ch;
}while(ch != '@');
 i = 0;
do{
  flag = Scan(program);
  if (flag == 200)
  {
printf("(%2d,%4d)",flag,number);
  }
  else if (flag == -1)
  {
printf("(%d,error)",flag);
  }
  else
  {
printf("(%2d,%4s)",flag,words);
  }
}while (flag != 0);
    system("pause");
}