编程实验一 词法分析程序

#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);
 }
 }
}