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);                        //读入源程序字符串到缓冲区，以#结束，允许多行输入
    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;
    }
    printf("\n\n备注:数字10代表所输入的不是关键词，只是普通词\n");
    printf("     数字20代表您输入的是数字\n");
    printf("     数字1000是结束标志\n\n");
 
}
 
//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);
            }
        }
    }