IF-ELSE条件语句的翻译程序设计(递归下降法、输出四元式)源码

//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
E->id > id


*/
#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 $LESS 248
#define $ID 254


typedef struct Wtoken
{
int type;

char ch;
}Wtoken;

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

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

Wtoken tokentable[MAX_TOKEN];
Fourtable 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 cifafenxi();
void print();

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

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

void printFourtable();
void main()
{
cout<<"Please input the name of file:";
char fname[200];
cin>>fname;
if(!init(fname))
return;
if(!cifafenxi())
return;
char ch;
while(1)
{
if(ins.eof())
break;
ins>>ch;
}
cout<<"The result of CIFA analyse :"<<endl;
print();
cout<<endl<<endl;
nexttoken();
cout<<"The Grammar:"<<endl;
yufafenxi();
cout<<"The FourTable as followings:"<<endl;
printFourtable();
}
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 cifafenxi()
{
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=$LESS;
}
else if(ch=='=')
{
tokentable[total_len++].type=$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_le
n].par2=npar2; quad[quad_len].address=naddress; quad_len++; }

Wtoken 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==$ID)
{
char a,b;
int mark=0;
a=cur.ch;
cout<<"E->"<<cur.ch;
if(!nexttoken())
ERROR("E()");
if(cur.type==$GREAT)
{cout<<'>';mark=1;}
else if(cur.type==$LESS)
cout<<'<';
else
ERROR("E()");

if(!nexttoken())
ERROR("E()");
if(cur.type!=$ID)
ERROR("E()");
cout<<cur.ch<<endl;
b=cur.ch;

if(mark==0)
AD_ADDRESS(begin,JL,a,b,etrue);
if(mark==1)
AD_ADDRESS(begin,JG,a,b,etrue);

AD_ADDRESS(-1,JUMP,0,0,efalse);
if(!nexttoken())
ERROR("E()");
}
else
ERROR("E()");
}

void yufafenxi()
{
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==$IF)
cout<<"IF"<<" "<<"关键字"<<endl;
if(tokentable[token_index].type==$ELSE)
cout<<"ELSE"<<" "<<"关键字"<<endl;
if(tokentable[token_index].type==$THEN)
cout<<"THEN"<<" "<<"关键字"<<endl;
if(tokentable[token_index].type==$ID)
cout<<tokentable[token_index].ch<<" "<<"标识符"<<endl;
if(tokentable[token_index].type==$ASSIGN)
cout<<'='<<" "

;<<"运算符"<<endl;
if(tokentable[token_index].type==$GREAT)
cout<<'>'<<" "<<"运算符"<<endl;
if(tokentable[token_index].type==$LESS)
cout<<'<'<<" "<<"运算符"<<endl;

}
token_index=0;
}

void printFourtable()
{
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<<"(>,"<<quad[i].par1<<","<<quad[i].par2<<",L"<<quad[i].address<<")"<<endl;
}
else if(quad[i].op==JL)
{
cout<<"(<,"<<quad[i].par1<<","<<quad[i].par2<<",L"<<quad
[i].address<<")"<<endl;
}
else if(quad[i].op==JUMP)
{
cout<<","<<"-,-,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;
}
}
}



//以下是输入文件内容
/*

IF (a<b) THEN
IF (c>d) THEN
x=f;
ELSE x=t;
ELSE
IF (b>y) THEN
x=y;
ELSE x=r;
*/