条件语句.cpp

递归下降方法完成的条件语句分析 包含设计报告

#include<iostream.h>
#include<fstream.h>
#include<string.h>


#define $ASSIGN 249
#define $IF 250
#define $THEN 251
#define $ELSE 252
#define $GREAT 253
#define $ID 254


//有效字符串: IF,ELSE,THEN, a,b,x,>,=


/*
文法:

  S->id=id | if E then S else S
  E->id < id

*/

typedef struct Token
{
	int type;
	char ch;
}Token;

typedef enum{JUMP,JG,ASSIGN,END}OpKind;
typedef struct
{
	int label;//标号
	OpKind op;
	char par1,par2;
	union{
		char result;
		int address;
	};
}Quad;//四元式

#define MAX_TOKEN 256 //Token表大小
#define MAX_QUAD 256 //四元式数组大小

Token tokentable[MAX_TOKEN];
Quad quad[MAX_QUAD];
int token_index;//token表索引
int total_len;//token表有效长度

int quad_len;//四元式表有效长度
int quad_index;//四元式索引

int label;
ifstream ins;

bool init(char filename[255]);
bool cifa();
void print();

void ERROR();
void S(int,int);

void E(int,int,int);
bool nexttoken();
int newlabel();
void yuyi();

void printQuad();
void main()
{
	cout<<"输入待编译文件名:";
	char fname[200];
	cin>>fname;
	if(!init(fname))
		return;
	if(!cifa())
		return;
	char ch;
	while(1)
	{
		if(ins.eof())
			break;
		ins>>ch;
	}
	cout<<"词法分析结果:"<<endl;
	print();
	cout<<endl<<endl;
	nexttoken();
	cout<<"所使用的产生式:"<<endl;
	yuyi();
	cout<<"四元式:"<<endl;
	printQuad();
}
int newlabel()
{
	return label++;
}
bool init(char filename[255])
{
	token_index=0;
	total_len=0;
	quad_len=0;
	quad_index=0;
	label=100;
	ins.open(filename,ios::nocreate | ios::in);
	if(ins.fail())
	{
		cout<<"文件打开出错!"<<endl;
		return false;
	}

	return true;
}
//

bool cifa()
{
	char buf[16];
	char ch;
	while(1)
	{
		ins>>ch;
		if(ins.fail())
			break;
		if(ch=='I')
		{
			ins>>buf;
			if(strcmp(buf,"F")==0)
				tokentable[total_len++].type=$IF;
		}
		else if(ch=='T')
		{
			ins>>buf;
			if(strcmp(buf,"HEN")==0)
				tokentable[total_len++].type=$THEN;
		}
		else if(ch=='E')
		{
			ins>>buf;
			if(strcmp(buf,"LSE")==0)
				tokentable[total_len++].type=$ELSE;
		}
		else if(ch=='>')
		{
			tokentable[total_len++].type=$GREAT;
		}
		else if(ch=='=')
		{
			tokentable[total_len++].type=$ASSIGN;
		}
		else if(ch=='x' || (ch>='a' && ch<='z'))
		{
			tokentable[total_len].type=$ID;
			tokentable[total_len++].ch=ch;
		}
	}
	return true;
	
}

#define AD_RESULT(nlabel,nop,npar1,npar2,nresult) {quad[quad_len].label=nlabel; quad[quad_len].op=nop; quad[quad_len].par1=npar1; quad[quad_len].par2=npar2; quad[quad_len].result=nresult; quad_len++; }
#define AD_ADDRESS(nlabel,nop,npar1,npar2,naddress) {	quad[quad_len].label=nlabel; 	quad[quad_len].op=nop; 	quad[quad_len].par1=npar1; 	quad[quad_len].par2=npar2; 	quad[quad_len].address=naddress; 	quad_len++; }

Token cur;
bool nexttoken()
{
	if(token_index>=total_len)
		return false;
	cur.type=tokentable[token_index].type;
	cur.ch=tokentable[token_index].ch;
	token_index++;
	return true;
}



void ERROR(char str[20])
{
	cout<<"error!  "<<str<<endl;
}

void S(int begin,int next)
{

	if(cur.type==$ID)
	{
		char a,b;
		cout<<"S->"<<cur.ch;
		a=cur.ch;
		if(!nexttoken())
			ERROR("S");
		if(cur.type!=$ASSIGN)
			ERROR("S");
		cout<<"=";
		if(!nexttoken())
			ERROR("S");
		if(cur.type!=$ID)
			ERROR("S");
		cout<<cur.ch<<endl;
		b=cur.ch;
		AD_RESULT(begin,ASSIGN,b,0,a);
		AD_ADDRESS(-1,JUMP,0,0,next);
		nexttoken();
	}
	else if(cur.type==$IF)
	{
		if(!nexttoken())
			ERROR("S");
		{
			cout<<"S->if E then S else S"<<endl;
			int etrue=newlabel();
			int efalse=newlabel();
			
			E(begin,etrue,efalse);
			if(cur.type==$THEN)
			{
				if(!nexttoken())
				ERROR("S");
				
				S(etrue,next);

				if(cur.type==$ELSE)
				{
					if(!nexttoken())
					ERROR("S");
					S(efalse,next);
				}
				else
				{
					ERROR("S");
				}
			}
			else
				ERROR("S");
		}
	}
}

void E(int begin,int etrue,int efalse)
{
	if(cur.type==$ID)
	{
		char a,b;
		a=cur.ch;
		cout<<"E->"<<cur.ch<<">";
		if(!nexttoken())
			ERROR("E()");
		if(cur.type!=$GREAT)
			ERROR("E()");
		if(!nexttoken())
			ERROR("E()");
		if(cur.type!=$ID)
			ERROR("E()");
		cout<<cur.ch<<endl;
		b=cur.ch;

		AD_ADDRESS(begin,JG,a,b,etrue);
		AD_ADDRESS(-1,JUMP,0,0,efalse);
		if(!nexttoken())
			ERROR("E()");
	}
	else
		ERROR("E()");
}

void yuyi()
{
	S(-1,1000);
	AD_RESULT(1000,END,0,0,'-');
}


void print()
{
	for(token_index=0;token_index<total_len;token_index++)
	{
		if(tokentable[token_index].type==$IF)
			cout<<"IF"<<endl;
		if(tokentable[token_index].type==$ELSE)
			cout<<"ELSE"<<endl;
		if(tokentable[token_index].type==$THEN)
			cout<<"THEN"<<endl;
		if(tokentable[token_index].type==$ID)
			cout<<tokentable[token_index].ch<<endl;
		if(tokentable[token_index].type==$ASSIGN)
			cout<<'='<<endl;
		if(tokentable[token_index].type==$GREAT)
			cout<<'>'<<endl;

	}
	token_index=0;
}

void printQuad()
{
	for(int i=0;i<quad_len;i++)
	{
		if(quad[i].label>-1)
			cout<<"L"<<quad[i].label<<":";
		else cout<<"     ";
		if(quad[i].op==JG)
		{
			cout<<"J>,"<<quad[i].par1<<","<<quad[i].par2<<",L"<<quad[i].address<<endl;
		}
		else if(quad[i].op==JUMP)
		{
			cout<<"J ,"<<"-,-,L"<<quad[i].address<<endl;
		}
		else if(quad[i].op==ASSIGN)
		{
			cout<<"= ,"<<quad[i].par1<<",-,"<<quad[i].result<<endl;
		}
		else if(quad[i].op==END)
		{
			cout<<"-,-,-,-"<<endl;
		}
	}
}