语法分析

#include<stdio.h>
#include<string.h>

char prog[80],token[6];
char ch;
int syn,p,m,n,sum,kk=0;
char * rwtab[6]={"begin","if","then","while","do","end"};
main()
{
 p=0;
 printf("\nplease intput string:");
do
{
 ch=getchar();
 prog[p++]=ch;
}while(ch!=‘#‘);
p=0;
scaner();
lrparser();
getch();
}

/*词法扫描程序：*/
scaner()
{
 for(n=0;n<8;n++)
  token[n]=NULL;
  m=0;
  ch=prog[p++];
  while(ch==‘ ‘)ch=prog[p++];
  if((ch<=‘z‘&&ch>=‘a‘)||(ch<=‘Z‘&&ch>=‘A‘))
  {
   while((ch<=‘z‘&&ch>=‘a‘)||(ch<=‘Z‘&&ch>=‘A‘)||(ch<=‘9‘&&ch>=‘0‘))
   {
    token[m++]=ch;
    ch=prog[p++];
    }
   token[m++]=‘\0‘;
   ch=prog[--p];
   syn=10;
   for(n=0;n<6;n++)
       if(strcmp(token,rwtab[n])==0)
       {
        syn=n+1;
        break;
        }
    }
   else
       if((ch<=‘9‘&&ch>=‘0‘))
         {
          sum=0;
          while((ch<=‘9‘&&ch>=‘0‘))
          {
           sum=sum*10+ch-‘0‘;
           ch=prog[p++];
           }
           ch=prog[--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;
                          ch=prog[--p];
                          }
          break;
          case ‘>‘:token[m++]=ch;
                   ch=prog[p++];
                   if(ch==‘=‘)
                   {
                   syn=24;
                   token[m++]=ch;
                    }
                   else
                   {
                    syn=23;
                    ch=prog[--p];
                    }
          break;
          case ‘:‘:token[m++]=ch;
                   ch=prog[p++];
                   if(ch==‘=‘)
                   {
                    syn=18;
                    token[m++]=ch;
                    }
                    else
                    {
                     syn=17;
                     ch=prog[--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=18;token[0]=ch;break;
          case ‘<>‘:syn=21;token[0]=ch;break;
          case ‘<=‘:syn=22;token[0]=ch;break;
          case ‘>=‘:syn=24;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;
          }
      }



lrparser()
{
 if(syn==1)
  {
   scaner();
   yucu();
   if(syn==6)
    {
     scaner();
     if((syn==0)&&(kk==0))
     printf("sucess");
     }
   else
     {
      if(kk!=1) printf("lost end error!");
      kk=1;
      }
    }
 else
 {
  printf("output of begin is error!");
  kk=1;
  }
  return;
}


yucu()
{
 statement();
  while(syn==26)
   {
    scaner();
    statement();
    }
    return;
}


statement()
{
 if(syn==10)
  {
   scaner();
   if(syn==18)
    {
    scaner();
     expression();
     }
   else
    {
     printf("output of equal is error!");
     kk=1;
    }
  }
  else
  {
   printf("input of sentence is error!");
   kk=1;
   }
   return;
  }



expression()
{
 term();
 while(syn==13||syn==14)
 {
  scaner();
  term();
  }
 return;
}


term()
{
 factor();
 while(syn==15||syn==16)
   {
    scaner();
    factor();
    }
 return;
}


factor()
{
 if(syn==10||syn==11)scaner();
 else
     if(syn==27)
     {
      scaner();
      expression();
      if(syn==28)scaner();
      else
       {
        printf("output ‘)‘ is error!");
        kk=1;
        }
      }
      else
      {
       printf("output expression is error!");
       kk=1;
       }
 return;
 }