词法分析.cpp

这是一个编译原理的词法分析的二元式表示程序

#include <stdio.h>
#include <conio.h>  //getch
#include <string.h>
#include <stdlib.h>  //exit(0)

char prog[80],token[8],ch;
int syn,p,m,n,sum;
char *rwtab[4]={"if","else","while","do"};
 scaner();
main()
{    p=0;
	 printf("\n please input a string(end with '#'):");
	 do{
		scanf("%c",&ch);
		prog[p++]=ch;
		}while(ch!='#');
	 p=0;
	 do{
		scaner();
		switch(syn)
		 {case 11:printf("( %-10d%5d )\n",sum,syn);
			  break;
		  case -1:printf("you have input a wrong string\n");
			  getch();
			  exit(0);
		  default: printf("( %-10s%5d )\n",token,syn);
			  break;
		  }
		}while(syn!=0);
		getch();
	 }
	 scaner()
	 {  sum=0;
		for(m=0;m<8;m++)token[m++]=NULL;
		ch=prog[p++];
		m=0;
		while((ch==' ')||(ch=='\n'))ch=prog[p++];
		if(((ch<='z')&&(ch>='a'))||((ch<='Z')&&(ch>='A')))
		  { while(((ch<='z')&&(ch>='a'))||((ch<='Z')&&(ch>='A'))||((ch>='0')&&(ch<='9')))
		  {token[m++]=ch;
		   ch=prog[p++];
		  }
		  p--;
		  syn=10;
		  for(n=0;n<6;n++)
		if(strcmp(token,rwtab[n])==0)
		   { syn=n+1;
			 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 '<':token[m++]=ch;
			  ch=prog[p++];
			   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=17;
				  token[m++]=ch;
				}
			  else
				{ syn=13;
				  p--;
				}
			  break;
		 case '-':token[m++]=ch;
			  ch=prog[p++];
			  if(ch=='-')
				{ syn=29;
				  token[m++]=ch;
				}
			  else
				{ syn=14;
				  p--;
				}
			  break;
		 case '!':ch=prog[p++];
			  if(ch=='=')
			   { syn=21;
				 token[m++]=ch;
			   }
			  else
			  { syn=31;
				 p--;
			  }
			  break;
		 case '=':token[m++]=ch;
			  ch=prog[p++];
			  if(ch=='=')
				{ syn=25;
				  token[m++]=ch;
				}
			  else
				{ syn=18;
				  p--;
				}
			  break;
		 case '*': syn=15;
			   token[m++]=ch;
			   break;
		 case '/': syn=16;
			   token[m++]=ch;
			   break;
		 case '(': syn=27;
			   token[m++]=ch;
			   break;
		 case ')': syn=28;
			   token[m++]=ch;
			   break;
		 case '{': syn=5;
			   token[m++]=ch;
			   break;
		 case '}': syn=6;
			   token[m++]=ch;
			   break;
		 case ';': syn=26;
			  token[m++]=ch;
			  break;
		 case '\"': syn=30;
			   token[m++]=ch;
			   break;
		 case '#': syn=0;
			   token[m++]=ch;
			   break;
		 case ':':syn=17;
			   token[m++]=ch;
			   break;
		default: syn=-1;
			 break;
		   }
		token[m++]='\0';
    }