cpp4.cpp

来自「这是一个C语言编写的实现的是对输入语句进行建单的词法分析的法分析器的源程序」· C++ 代码 · 共 206 行

#include<stdio.h>
#include<string.h>
#include<iostream.h>
char prog[80],token[8];
char ch;
void scaner();
void lrparser();
void yucu();
void statement();
void expression();
void term();
void factor();
int syn,p,m,n,sum;int kk=0;
char *rwtab[6]={"begin","if","then","while","do","end"};
void main()
{
	p=0;
	printf("\n please input string:\n");
	do{
		ch=getchar();
	    prog[p]=ch;
	    p++;
	}while(ch!='#');
	p=0;
	
		scaner();
		lrparser();
	
}
void scaner()
{ 
	m=0;
	for(n=0;n<8;n++)token[n]=NULL;
	ch=prog[p++];
	while(ch==' ')
	    ch=prog[p++];
	if(ch>='a'&&ch<='z')
	{
		while(ch>='a'&&ch<='z'||ch>='0'&&ch<='9')
		{	token[m++]=ch;
		    ch=prog[p++];
		}
	token[m++]='\0';p--;syn=10;
	for(n=0;n<6;n++)
		if(strcmp(token,rwtab[n])==0)
		{
			switch(n)
			{
			case 0 :syn=1;	break;
			case 1 :syn=2;	break;
			case 2 :syn=3;	break;
			case 3 :syn=4;	break;
			case 4 :syn=5;	break;
			case 5 :syn=6;	break;
			}
		}
	}
    else
    if(ch>='0'&&ch<='9')
	{
		while(ch>='0'&&ch<='9')
		{
			sum=sum*10+ch-'0';
			ch=prog[p++];
		}
		p--;syn=11;
	}
	else
		switch(ch)
	{
		case'<' :m=0;token[m++]=ch;
			ch=prog[p++];
			if(ch=='>')
			{
				syn=21;
				token[m++]=ch;
			}
			else if(ch=='=')
			{
				syn=22;
				token[m++]=ch;
			}
			else
			{
				syn=20; p--;
			}
			break;
		case'>' :token[m++]=ch;
			ch=prog[p++];
			if(ch=='=')
			{
				syn=24;
		
			token[m++]=ch;
			}
			else
			{
				syn=23;
				p--;
			}
			break;
		case':' :token[m++]=ch;
			ch=prog[p++];
			if(ch=='=')
			{
				syn=18;
				token[m++]=ch;
			}
			else
			{
				syn=17;
				p--;
			}
			break;
		case'+' :syn=13;token[0]=ch;break;
		case'-' :syn=14;token[0]=ch;break;
		case'*' :syn=15;token[0]=ch;break;
		case'/' :syn=16;token[0]=ch;break;
	    case'=' :syn=25;token[0]=ch;break;
		case';' :syn=26;token[0]=ch;break;
		case'(' :syn=27;token[0]=ch;break;
		case')' :syn=28;token[0]=ch;break;
		case'#' :syn=0;token[0]=ch;break;
		default:syn=-1;
	}
}
void lrparser()
{
	if(syn==1)
	{
		scaner();
		yucu();
		if(syn==6)
		{
			scaner();
			if((syn==0)&&(kk==0))
				printf("success");
		}
		else{if(kk!=1)cout<<"no end;error";kk=1;}
	}
	else{printf("no begin;error");kk=1;}
	return;
}
void yucu()
{
	statement();
	while(syn==26)
	{
		scaner();
		statement();
	}
	return;
}
void statement()
{
	if(syn==10)
	{
		scaner();
		if(syn==18)
		{
			scaner();
			expression();
		}
		else{printf("赋值号错误");kk=1;}
	
	}
	else{printf("输出语句错误");kk=1;}
	return;
}
void expression()
{
	term();
	while(syn==13||syn==14)
	{
		scaner();
		term();
	}
	return;
}
void term()
{
	factor();
	while(syn==15||syn==16)
	{
		scaner();
		factor();
	}
	return;
}
void factor()
{
	if(syn==10||syn==11)
		scaner();
	else if(syn=27)
	{
		scaner();
		expression();
		if(syn==28)
		   scaner();
		else{printf("')'错误");kk=1;}
	}
	else{printf("表达式错误");kk=1;}
	return;
}