编译原理（第三版） 语法分析器

语法分析器在词法分析器的基础上增加了递归下降分析程序，咱也不知道啥是递归下降程序，咱也不想问。
但是有程序框图和伪代码把程序跑通咱还是比较在行滴。为了便于理解，debug过程中的输出也保留了。

下面是完整代码。

/*
    begin a:= 9; x:=2*3;b:=a+x end#
    x:= a+b*c end #
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define _KEY_WORD_END "waiting for your expanding"
typedef struct
{
    int typenum;
    char *word;
}WORD;
char input[255];
char token[255]="";
int p_input;
int p_token;
char ch;
char* rwtab[] = {"begin","if","then","while","do","end",_KEY_WORD_END};
WORD * scaner();
WORD* oneword = new WORD;
int syn,kk;
void expression();
void factor()
{
    if(syn == 10 || syn == 11)
    {
        oneword = scaner();
        syn = oneword->typenum;
        printf("%s   %d
",oneword->word,syn);
    }
    else if(syn == 27)
    {
        oneword = scaner();
        syn = oneword->typenum;
        printf("%s   %d
",oneword->word,syn);
        expression();
        if(syn == 28)
        {
            oneword = scaner();
            syn = oneword->typenum;
            printf("%s   %d
",oneword->word,syn);
        }
        else{
            printf("右括号错误
");
            kk = 1;
        }
    }
    else
    {
        printf("表达式错误
");
        kk = 1;
    }
    return;
}
void term()
{
    factor();
    while(syn == 15 || syn == 16)
    {
        oneword = scaner();
        syn = oneword->typenum;
        printf("%s   %d
",oneword->word,syn);
        factor();
    }
    return;
}
void expression()
{
    term();
    while(syn == 13 || syn == 14)
    {
        oneword = scaner();
        syn = oneword->typenum;
        printf("%s   %d
",oneword->word,syn);
        term();
    }
    return;
}
void statement()
{
    if(syn == 10)
    {
        oneword = scaner();
        syn = oneword->typenum;
        printf("%s   %d
",oneword->word,syn);
        if(syn == 18)
        {
            oneword = scaner();
            syn = oneword->typenum;
            printf("%s   %d
",oneword->word,syn);
            expression();
        }
        else{
            printf("赋值号错误
");
            kk = 1;
        }
    }
    else{
        printf("语句错误
");
        kk = 1;
    }
    return;
}
void yucu()
{
    statement();
    while(syn == 26)
    {
        oneword = scaner();
        syn = oneword->typenum;
        printf("%s   %d
",oneword->word,syn);
        statement();
    }
    return;
}
void Irparser()
{
    if(syn == 1)
    {
        oneword = scaner();
        syn = oneword->typenum;
        printf("%s   %d
",oneword->word,syn);
        yucu();

        if(syn==6)
        {
            oneword = scaner();
            syn = oneword->typenum;
            if(syn == 0 && (kk == 0))
                printf("success
");
        }
        else{
            if(kk != 1)
            {
                printf("缺少end错误
");
                kk = 1;
            }
        }
    }
    else{
        printf("begin错误
");
        kk = 1;
    }
    return;
}
int main()
{
    int over = 1;

    printf("Enter Your words(end with #):");
    scanf("%[^#]s",input);
    p_input = 0;
    printf("Your words:
%s
",input);

        //获取下一个单词符号
        oneword = scaner();
        syn = oneword->typenum;
        Irparser();

    printf("
press # to exit:");
    scanf("%[^#]s",input);
    return 0;
}
char m_getch()
{
    ch = input[p_input];
    p_input = p_input+1;
    return(ch);
}
void getbc()
{
    while(ch == ' '||ch == 10)
    {
        ch = input[p_input];
        p_input++;
    }
}
void concat()
{
    token[p_token] = ch;
    p_token++;
    token[p_token] = '';
}
int letter()
{
    if((ch >= 'a'&& ch <= 'z')|| (ch >='A'&&ch <= 'Z'))
        return 1;
    else
        return 0;
}
int digit()
{
    if(ch >= '0'&&ch <='9')return 1;
    else return 0;
}
int reserve()
{
    int i = 0;
    while(strcmp(rwtab[i],_KEY_WORD_END))
    {
        if(!strcmp(rwtab[i],token))
            return i+1;
        i++;
    }
    return 10;
}
void retract()
{
    p_input--;
}

char* dtb()
{
    return NULL;
}

WORD* scaner()
{

    WORD* myword = new 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 = 11;
        myword->word = token;
        return(myword);
    }
    else switch(ch)
    {
        case'=':m_getch();
            if(ch == '=')
            {
                myword->typenum = 25;
                myword->word = "==";
                return(myword);
            }
            retract();
            myword->typenum = 21;
            myword->word = "=";
            return(myword);
            break;
        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'(':
            myword->typenum = 27;
            myword->word = "(";
            return(myword);
            break;
        case')':
            myword->typenum = 28;
            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':':m_getch();
            if(ch == '=')
            {
                myword->typenum = 18;
                myword->word = ":=";
                return(myword);
            }
            retract();
            myword->typenum = 17;
            myword->word = ":";
            return(myword);
            break;
        case';':
            myword->typenum = 26;
            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'<':m_getch();
            if(ch == '=')
            {
                myword->typenum = 22;
                myword->word = "<=";
                return(myword);
            }
            else if(ch == '>')
            {
                myword->typenum = 21;
                myword->word = "<>";
                return(myword);
            }
            retract();
            myword->typenum = 20;
            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'#':
            myword->typenum = 0;
            myword->word = "#";
            return(myword);
            break;
        case'':
            myword->typenum = 0;
            myword->word = "OVER";
            return(myword);
            break;
        default: myword->typenum = -1;
            myword->word = "ERROR";
            return(myword);
    }
}