#include<stdio.h> //包含库所用的某些宏和变量
#include<stdlib.h> //包含库
#include<string.h> //包含字符串处理库
#define _KEY_WORD_END "waiting for your expanding" //定义关键字结束标志
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_WORD_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("输入源代码(以 #结束):"); //读入源程序字符串到缓冲区，以#结束，允许多行输入
scanf("%[^#]s",input);
p_input=0;
printf("Your words:%s ",input);
while(over<1000&&over!=-1)
{
oneword=scaner();
printf("单词符号:%s 种别码:%d ",oneword->word,oneword->typenum);
over=oneword->typenum;
}
}
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]=' ';
}
//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;
while(strcmp(rwtab[i],_KEY_WORD_END))
{
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 '+':
myword->typenum=13;
myword->word="+";
return(myword);
break;
case '-':
myword->typenum=14;
myword->word="-";
return(myword);
break;
case '*':
myword->typenum=15;
myword->word="*";
return(myword);
break;
case '/':
myword->typenum=16;
myword->word="/";
return(myword);
break;
case ':': m_getch();
if(ch=='='){
myword->typenum=18;
myword->word=">=";
return(myword);
}
retract();
myword->typenum=17;
myword->word=":";
return(myword);
break;
case '<': m_getch();
if(ch=='='){
myword->typenum=21;
myword->word="<=";
return(myword);
}
else if(ch=='>'){
myword->typenum=22;
myword->word="<>";
return(myword);
}
retract();
myword->typenum=20;
myword->word="<";
return(myword);
break;
case '>': m_getch();
if(ch=='='){
myword->typenum=24;
myword->word=">=";
return(myword);
}
retract();
myword->typenum=23;
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=0;
myword->word="OVER";
return(myword);
break;
default:
myword->typenum=-1;
myword->word="ERROR";
return(myword);
}
}
}