递归下降分析法.txt

利用高级语言的递归过程为给定文法的每个非终结符构造对应的递归函数

#include "fstream.h"
#include "iostream.h"
#include "stdlib.h"
struct code_val{
	char code;char val[20];
} t; //定义临时结构变量，存放单词二元式。
ifstream cinf("lex_r.txt",ios::in); 		//从文件lex_r.txt输入数据
ofstream coutf("par_r.txt",ios::out);		//结果输出至文件par_r.txt
void E(void);
void F(void)		//F→(E)|i|x|y
{
	if(t.code=='i'||t.code=='x'||t.code=='y')
    { 
		cinf>>t.code>>t.val;coutf<<t.code; 	//读一个单词的二元式并输出单词种别
    }
	else 
		if(t.code=='(')
		{
			cinf>>t.code>>t.val;coutf<<t.code;  	//读一个单词的二元式并输出单词种别
			E( );
			if(t.code==')')
			{
				cinf>>t.code>>t.val;coutf<<t.code;	//读一个单词的二元式并输出单词种别
			}
			else{
				coutf<<"Err in F1>"<<t.code<<endl;exit(0);
			}
		}
		else{
			coutf<<endl<<"Err in F2>"<<t.code<<endl;exit(0);
		}
}
void T1(void)		//T'→*FT'|ε
{
	if(t.code=='*')
	{
		cinf>>t.code>>t.val;coutf<<t.code; 	//读一个单词的二元式并输出单词种别
		F( );T1( );
	}
	else 
		if(!(t.code=='#'||t.code==')'||t.code=='+'))
        { 
			coutf<<endl<<"Err in T1()>"<<t.code<<endl;exit(0);
		}
}
void T(void)		//T→FT'
{
	if(t.code=='i'||t.code=='x'||t.code=='y'||t.code=='(')
	{
		F( );T1( );
	}
	else{
		coutf<<endl<<"Err in T()>"<<t.code<<endl;exit(0);
	}
}
void E1(void)		//E'→+TE'|ε
{
   if(t.code=='+')
   {
	   cinf>>t.code>>t.val;coutf<<t.code; 	//读一个单词的二元式并输出单词种别
	   T( );E1( );
   }
   else 
      if(!(t.code=='#'||t.code==')'))
		  coutf<<endl<<"Err in E1()>"<<endl<<t.code;
}
void E(void)	                        	//E→T E'
{	
	if(t.code=='i'||t.code=='x'||t.code=='y'||t.code=='(')
	{
		T( );E1( );
	}
	else
	{
		coutf<<endl<<"Err in E()>"<<t.code<<endl;exit(0); 
	}
}
void main(void)
{
	cinf>>t.code>>t.val;coutf<<t.code; 		//读一个单词的二元式并输出单词种别
	E( );
	if(t.code=='#')
		coutf<<endl<<"ok"<<endl;
	else
		coutf<<endl<<"err in main()"<<endl;
}