// Lex.cpp : Defines the entry point for the console application.
//
#include “stdafx.h”
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <process.h>
//P83 3.4.2保留字和标识符的识别
//初始化时就将各个保留字填入符号表中
const char* KEYWORD[6] = {“begin”, “if”, “then”, “while”, “do”, “end”};
char buffer[1024] = {0};//输入缓冲区
char token[10] = {0};//词素，数组大小限制着标识符的长度。
int forward = 0, syn = -1;//游标和种别码
void analyzer();
int main(int argc, char* argv[])
{
//输入，以#结束。
printf(“请输入：（示例输入begin x:=9;if x>0 then x:=2*x+1/3;end#）\n”);
char input;
do
{
input = getchar();
buffer[forward++] = input;
}
while(input != ‘#’);
//分析，以#的种别码0结束。
forward = 0;
do
{
analyzer();
printf(“(%d, %s)\n”, syn, token);
}
while(syn != 0);
system(“pause”);
return 0;
}
void analyzer()
{
memset(token, ‘\0’, sizeof(token));//清空前一个已分析的词素
char ch = buffer[forward++];//当前分析的字符
while(isspace(ch))//忽略空格
ch = buffer[forward++];
switch(ch)
{
case ‘+’:
token[0] = ch;
syn = 13;
return;
case ‘-‘:
token[0] = ch;
syn = 14;
return;
case ‘*’:
token[0] = ch;
syn = 15;
return;
case ‘/’:
token[0] = ch;
syn = 16;
return;
case ‘:’:
token[0] = ch;
if(buffer[forward] == ‘=’)
{
forward++;
token[1] = ‘=’;
syn = 18;
}
else
syn = 17;
return;
case ‘<‘:
token[0] = ch;
if(buffer[forward] == ‘>’)
{
forward++;
token[1] = ‘>’;
syn = 21;
}
else if(buffer[forward] == ‘=’)
{
forward++;
token[1] = ‘=’;
syn = 22;
}
else
syn = 20;
return;
case ‘>’:
token[0] = ch;
if(buffer[forward] == ‘=’)
{
forward++;
token[1] = ‘=’;
syn = 24;
}
else
syn = 23;
return;
case ‘=’:
token[0] = ch;
syn = 25;
return;
case ‘;’:
token[0] = ch;
syn = 26;
return;
case ‘(‘:
token[0] = ch;
syn = 27;
return;
case ‘)’:
token[0] = ch;
syn = 28;
return;
case ‘#’:
token[0] = ch;
syn = 0;
return;
default:
int i = 0;
if(isdigit(ch))//数字
{
while(isdigit(ch))
{
token[i] = ch;
ch = buffer[forward++];
i++;
}
forward–;
syn = 11;
return;
}
else if(isalpha(ch))//字符组成保留字或标识符
{
while(isalnum(ch))
{
token[i] = ch;
ch = buffer[forward++];
i++;
}
forward–;
for(int j = 0; j < 6; j++)
{
if(strcmp(token, KEYWORD[j]) == 0)
{
syn = j + 1;
return;
}
}
syn = 10;
return;
}
}
}
