111.c

算术表达式的语法分析! 算术表达式的语法分析!

#include "stdio.h"
#include "string.h"  ；  语法分析
char prog[100],token[8],ch;
char *rwtab[6]={"begin","if","then","while","do","end"};
int syn,p,m,n,sum;
int kk;
factor();
expression();
yucu();
term();
statement();
lrparser();
scaner();
main()
{
 p=kk=0;
 printf("\nplease input a string (end with '#'): ");
 do
  { scanf("%c",&ch);
    prog[p++]=ch;
  }while(ch!='#');
 p=0;
 scaner();
 lrparser();
 getch();
}
lrparser()
{
 if(syn==1)
  { scaner();
    yucu();
    if (syn==6)
      { scaner();
 if ((syn==0)&&(kk==0)) printf("the analysis is success!\n");
 }
    else { if(kk!=1) printf("the string haven't got a 'end'!\n");
    kk=1;
  }
   }
 else { printf("haven't got a 'begin'!\n");
 kk=1;
      }
 return;
}
yucu()
{ statement();
 while(syn==26)
  { scaner();
   if(syn!=6) statement();
  }
 return;
}
statement()
{ if(syn==10)
  { scaner();
    if(syn==18)
      { scaner();
 expression();
      }
    else { printf("the sing ':=' is wrong!\n");
    kk=1;
   }
  }
 else { printf("wrong sentence!\n");
 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("the error on '('\n");
     kk=1;
    }
   }
 else { printf("the expression error!\n");
 kk=1;
      }
 return;
}
 scaner()
 { sum=0;
   for(m=0;m<8;m++)token[m++]=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>='0')&&(ch<='9')))
  {token[m++]=ch;
   ch=prog[p++];
  }
     p--;
     syn=10;
     token[m++]='\0';
     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 '<':m=0;
   ch=prog[p++];
   if(ch=='>')
     { syn=21;
     }
   else if(ch=='=')
     { syn=22;
     }
   else
     { syn=20;
        p--;
     }
   break;
 case '>':m=0;
   ch=prog[p++];
   if(ch=='=')
     { syn=24;
     }
   else
     { syn=23;
       p--;
     }
   break;
 case ':':m=0;
   ch=prog[p++];
   if(ch=='=')
     { syn=18;
     }
   else
     { syn=17;
       p--;
     }
   break;
 case '+': syn=13; break;
 case '-': syn=14; break;
 case '*': syn=15;break;
 case '/': syn=16;break;
 case '(': syn=27;break;
 case ')': syn=28;break;
 case '=': syn=25;break;
 case ';': syn=26;break;
 case '#': syn=0;break;
 default: syn=-1;break;
      }

    getch();
}