recuredesent.cpp

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// RecureDesent.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include<stdio.h>
#include<string.h>
#define xz sym=adv()

//////////////////////////////////////////////////////////////////////////////////////////////////
// 0-20  　 21    　　22  23  24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 
// 保留词　非保留词　数字　,  ;  :   .  (  )  [  ]  .. 无无  +  -  *  / 无  <  >  无 <= >= := {  }  #     
//////////////////////////////////////////////////////////////////////////////////////////////////

FILE *fp1;
char ch;
int sym;

void error()
{
	printf("%d error!\n ",sym);
}

int chz(char str1[15])//将str1[15]中的字符映射成小写并判断是否为str[21][15]中的单词
{
	char str[21][15]={"and","begin","const","div","do","else",
		   "end","function","if","integer","not","or","procdure",
	        "program","read","real","then","type",
			"var","while","write"};
	int i,max,min,mid;
	for(i=0;i<=14;i++)
		if(str1[i]<='Z'&&str1[i]>='A')
			str1[i]=str1[i]+'a'-'A';
    max=20;
	min=0;
	mid=10;
    while(min<=max)
	{	
		i=strcmp(str1,str[mid]);
		if(i==0) return mid;
		else if(i>0){min=mid+1;mid=(max+min)/2;}
		else {max=mid-1;mid=(max+min)/2;}
	}
	return 0;
}

int adv()//递归
{
	char str1[15];
	int t,i=0,sk=0;
    float num,xs;
    if(ch==' '||sym==24){fscanf(fp1,"%c",&(ch));printf("%c",ch);}//如果ch为空或sym为;即24则读取下一个字符
	while(!feof(fp1)&&i<100)
	{
		if(((ch)>='a'&&(ch)<='z')||((ch)>='A'&&(ch)<='Z'))//如果字符为字母则放入str1[i]中
		{
			i=0;
			while((((ch)>='a'&&(ch)<='z')||((ch)>='A'&&(ch)<='Z')||((ch)>='0'&&(ch)<='9')))
			{
				str1[i]=(ch);
				i++;
                {fscanf(fp1,"%c",&(ch));printf("%c",ch);}
			}
			str1[i]='\0';

			t=chz(str1);
             if(!t)return 21;//非保留词返回21
			 else return t;
		}
        else if(ch>='0'&&ch<='9')//如果字符为数字则将字符转化为数值num
		{
			num=0;
			while(ch>='0'&&ch<='9')
			{
				num=num*10+(ch)-'0';
				{fscanf(fp1,"%c",&(ch));printf("%c",ch);}

			}
			if(ch=='.')
			{
				xs=(float)0.1;
				{fscanf(fp1,"%c",&(ch));printf("%c",ch);}
                while(ch>='0'&&ch<='9')
				{
					num+=(ch-'0')*xs;
					xs*=(float)0.1;
					{fscanf(fp1,"%c",&(ch));printf("%c",ch);}
				}
			}
			return 22;
		}


		switch(ch)
		{
		    case '+' :{ch=' ';return 34;}
			case '*' :{ch=' ';return 36;}
		    case ',' :{ch=' ';return 23;}
		    case ';' :{ch=' ';return 24;}
		    case '.' :{ch=' ';return 26;}
		    case '(' :{ch=' ';return 27;}
            case ')' :{ch=' ';return 28;}
            case '[' :{ch=' ';return 29;}
			case ']' :{ch=' ';return 30;}
			case '{' :{ch=' ';return 45;}
			case '}' :{ch=' ';return 46;}
            case '-' :{ch=' ';return 35;}
            case '..' :{ch=' ';return 31;}
            case '/' :{ch=' ';return 37;}
			case '#' :{ch=' ';return 47;}
			case '<' :
				{
                    {fscanf(fp1,"%c",&(ch));printf("%c",ch);}sk=1;
					if((ch)=='=')
					{ch=' ';return 42;}
					else {return 39;}
				}
            case ':'  :
				{
                    {fscanf(fp1,"%c",&(ch));printf("%c",ch);}
					sk=1;
					if((ch)=='=')
						 {ch=' ';return 44;}
					else {return 25;}
				}
			  case '>'  :
				{
                    {fscanf(fp1,"%c",&(ch));printf("%c",ch);}
					sk=1;
					if((ch)=='=')
					{ch=' ';return 43;}
					else {return 40;}
				}
		    default:break;
		}
		if(sk==0){fscanf(fp1,"%c",&(ch));printf("%c",ch);}
		else sk=0;
	}
	return 48;//超出范围
}

void F();

void T()//"*  /"
{
	F();
	while(sym==36||sym==37)
	{
		xz;
		F();
	}
}
void E()//"+  -"
{
	T();
    while(sym==34||sym==35)
	{
		xz;
		T();
	}
}

void F()
{
	if(sym==21||sym==22) xz;//"非保留词　数字"
	else if(sym==27)//"( "
	{
		xz;
		E();
		if(sym==28) xz;//" )"
		else error();
	}
	else error();
}

void sentence();//对句子进行语法分析

void CS()//";　end"
{
	xz;
	sentence();
	while(sym==24)
	{
		xz;
		sentence();
	}
	if(sym==6)xz;
	else error();
}
void CT()//"else"
{
	if(sym==5)
	{
		xz;
		sentence();
	}
}
void EB()//逻辑运算< <= > >=
{
	E();
	if(sym<=43&&sym>=38)
	{
		xz;
		E();
	}
   else error();
}
void IT()//非保留词
{
	if(sym!=21)error();
	xz;
	while(sym==23)
	{
		xz;
		if(sym!=21)error();
		else error();
	}
}
void ET()// ,
{
	E();
	while(sym==23)
	{
		xz;
		E();
	}
}


void sentence()
{
	switch(sym)
	{
	case 21 :
		{
			xz;
			if(sym==44)//:=
			{
			xz;
			E();}
			else error();break;
		}
    case 1:CS();break;//begin
	case 8://if
		{
			xz;
			EB();
            if(sym!=5)error();//else
			xz;
             sentence();break;
		}
	case 19://while
		{
			xz;
			EB();
			if(sym!=4)error();//do
			xz;
			sentence();
		}break;
    case 14://read
		{
			xz;
			if(sym!=27) error();//(
			xz;
			IT();
			if(sym!=28)error();//)
			xz;break;
		}
     case 20://write
		{
			xz;
			if(sym!=27) error();//(
			xz;
			ET();
			if(sym!=28)error();//)
			xz;break;
		}

	}

}




int main(int argc, char* argv[])
{
	void CS();//end
	int chz(char str[15]);//将str1[15]中的字符映射成小写并判断是否为str[21][15]中的单词
	int adv();//递归
	void CT();//else
	void E();//+  -

	void EB();//< <= > >=
	void error();
	void ET();//,
	void F();//(  )
	void IT();//非保留词
	void T();// * /

    void sentence();//对句子进行语法分析

	ch=' ';
	fp1=fopen("pas.txt","r");
	if(!fp1){printf("cannot open pas.txt!!\n");}
     xz;
	sentence();

    fclose(fp1);
	return 0;
}