0921词法分析

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define _KEY_WOED_END "waiting for your expanding" //关键字结束标志

typedef struct
{
int typenum;
char * word;
}WORD;

char input[255]; //输入换缓冲区

char token[255]=""; //单词缓冲区

int p_input; //输入换缓冲区指针

int p_token; //单词缓冲区指针

char ch; //当前所读的字符

char *rwtab[]={"begin","if","then","while","do","end",_KEY_WOED_END}; //C语言关键字

WORD * scaner(); //词法扫描函数，获得关键字

main()
{
int over=1;
WORD *oneword;
oneword=(WORD *)malloc(sizeof(WORD));
printf("请输入您的字符串（以#作为结束标志）:");
scanf("%[^#]s",input); 
p_input=0;
printf("您输入的字符串是:%s\n\n",input);
while(over<1000&&over!=-1)
{
oneword=scaner();
printf("(%d,%s)\n",oneword->typenum,oneword->word);
over=oneword->typenum;
}

}

//需要用到的自编函数参考实现
//从输入缓冲区读取一个字符到ch中

char m_getch(){
ch=input[p_input];
p_input=p_input+1;
return (ch);
}

//去掉空白字符
void getbc()
{
while(ch==‘ ‘||ch==10){
ch=input[p_input];
p_input=p_input+1;
}
}

//拼接单词
void concat()
{
token[p_token]=ch;
p_token=p_token+1;
token[p_token]=‘\0‘;
}

//判断是否字母
int letter()
{
if(ch>=‘a‘&&ch<=‘z‘||ch>=‘A‘&&ch<=‘Z‘)return 1;
else return 0;
}

//判断是否数字
int digit()
{
if(ch>=‘0‘&&ch<=‘9‘)
return 1;
else
return 0;
}

//检索关键字表格
int reserve()
{
int i=0;
for(i=0;i<7;i++)
{
if(!strcmp(rwtab[i],token))
{
return i+1;
}
i=i+1;
}
return 10;
}

//回退一个字符
void retract()
{
p_input=p_input-1;
}

WORD *scaner()
{
WORD *myword;
myword=(WORD *)malloc(sizeof(WORD));
myword->typenum=10;
myword->word="";
p_token=0;
m_getch();
getbc();
if(letter())
{
while(letter()||digit())
{
concat();
m_getch();

}
retract();
myword->typenum=reserve();
myword->word=token;
return(myword);
}
else if(digit())
{
while(digit())
{
concat();
m_getch();
}
retract();
myword->typenum=20;
myword->word=token;
return(myword);
}
else
{
switch(ch)
{
case ‘=‘:m_getch();
if(ch==‘=‘)
{
myword->typenum=39;
myword->word="==";
return(myword);
}
retract();
myword->typenum=21;
myword->word="=";
return(myword);
break;
case ‘+‘:
myword->typenum=22;
myword->word="+";
return(myword);
break;
case ‘-‘:
myword->typenum=23;
myword->word="-";
return(myword);
break;
case ‘*‘:
myword->typenum=24;
myword->word="*";
return(myword);
break;
case ‘/‘:
myword->typenum=25;
myword->word="/";
return(myword);
break;
case ‘(‘:
myword->typenum=26;
myword->word="(";
return(myword);
break;
case ‘)‘:
myword->typenum=27;
myword->word=")";
return(myword);
break;
case ‘[‘:
myword->typenum=28;
myword->word="[";
return(myword);
break;
case ‘]‘:
myword->typenum=29;
myword->word="]";
return(myword);
break;
case ‘{‘:
myword->typenum=30;
myword->word="{";
return(myword);
break;
case ‘}‘:
myword->typenum=31;
myword->word="}";
return(myword);
break;
case ‘,‘:
myword->typenum=32;
myword->word=",";
return(myword);
break;
case ‘:‘:
myword->typenum=33;
myword->word=":";
return(myword);
break;
case ‘;‘:
myword->typenum=34;
myword->word=";";
return(myword);
break;
case ‘>‘:
myword->typenum=35;
myword->word=">";
return(myword);
break;
case ‘<‘:
myword->typenum=36;
myword->word="<";
return(myword);
break;
case ‘!‘:
m_getch();
if(ch==‘=‘)
{
myword->typenum=40;
myword->word="!=";
return(myword);
}
retract();
myword->typenum=-1;
myword->word="ERROR";
return(myword);
break;
case ‘\0‘:
myword->typenum=1000;
myword->word="OVER";
return(myword);
break;
default:
myword->typenum=-1;
myword->word="ERROR";
return(myword);
}
}
}