递归下降语法分析器.txt

用C++实现算符优先分析程序 用C++实现算符优先分析程序

＃i nclude "stdio.h"
＃i nclude "malloc.h"

struct Lchar{
 char char_ch;
 struct Lchar *next;
}Lchar,*p,*h,*temp,*top,*base;

int table[8][8]={{1,1,-1,-1,-1,1,-1,1},
    {1,1,-1,-1,-1,1,-1,1},
    {1,1,1,1,-1,1,-1,1},
    {1,1,1,1,-1,1,-1,1},
    {-1,-1,-1,-1,-1,-1,-1,0},
    {1,1,1,1,0,1,0,1},
    {1,1,1,1,0,1,0,1},
    {-1,-1,-1,-1,-1,0,-1,-1}};
/*存储算符优先关系表，大于为1，小于或等于为-1，其它为0表示出错*/

char curchar;
char curcmp;
int right;/*设置开关项，当出错时为0*/
int i,j;
int k;/*比较字符在栈的位置*/

void push(char pchar)/*入栈函数*/
{
 temp=malloc(sizeof(Lchar));
 temp->char_ch=pchar;
 temp->next=top;
 top=temp;
}

void pop(void)/*出栈函数*/
{
 if(top->char_ch!='#')
  top=top->next;
}

int changchartoint(char ch)/*将字符转为数字，以得到算符优先值*/
{
 int t;
 switch(ch)
 {
  case '+':t=0;break;
  case '-':t=1;break;
  case '*':t=2;break;
  case '/':t=3;break;
  case '(':t=4;break;
  case ')':t=5;break;
  case 'i':t=6;break;
  case '#':t=7;
 }
 return t;
}

void dosome(void)
{
 k=1;
 for(;;)
 {
  curchar=h->char_ch;
  temp=top;
  for(;;)
  {
   if(temp->char_ch=='N')
   {
    temp=temp->next;
    k++;
   }
   else
   {
    curcmp=temp->char_ch;
    break;
   }
  }
  printf("\n%d\t%d\t",table[i][j],k);
  temp=top;
  for(;;)/*打印栈*/
  {
   printf("%c",temp->char_ch);
   if(temp->char_ch=='#')
    break;
   else
    temp=temp->next;
  }
  printf("\t");
  temp=h;
  for(;;)/*打印待比较的字符*/
  {
   printf("%c",temp->char_ch);
   
   if(temp->char_ch=='#')
    break;
   else
    temp=temp->next;
  }
  i=changchartoint(curcmp);
  j=changchartoint(curchar);
  if(table[i][j]==0)/*算符优先值为空*/
  {
   printf("\n%d\t%d\t%c\t%c\terror1",table[i][j],k,curcmp,curchar);
   right=0;
   break;
  }
  else/*算符优先值不为空*/
  {
   if(table[i][j]<0)/*算符优先值为-1，移进*/
   {
    if(curchar=='#')/*待比较字符为空*/
    {
     if(k==2)/*当前比较字符在栈的位置为两个元素*/
      break;
     else
     {
      printf("\n%d\t%d\t%c\t%c\terror2",table[i][j],k,curcmp,curchar);
      right=0;
      break;
     }
    }
    push(curchar);
    k=1;
    curcmp=curchar;
    h=h->next;
   }
   else/*算符优先值为1，归约*/
   {
    if(curcmp=='i')/*当前比较为i,出栈一次*/
     pop();
    else/*当前比较不为i,出栈三次*/
    {
     pop();
     pop();
     pop();
    }
    push('N');/*归约到N*/
    k=1;
   }
  }
 }
}
void main(void)
{
 char ch;
 right=1;
 base=malloc(sizeof(Lchar));
 base->next=NULL;
 base->char_ch='#';
 top=base;
 h=malloc(sizeof(Lchar));
 h->next=NULL;
 p=h;
 do{    /*输入待比较字符串，以'#'结束*/
  ch=getch();
  putch(ch);
  if(ch=='i'||ch=='+'||ch=='-'||ch=='*'||ch=='/'||ch=='('||ch==')'||ch=='#')
  {
   temp=malloc(sizeof(Lchar));
   temp->next=NULL;
   temp->char_ch=ch;
   h->next=temp;
   h=h->next;
  }
  else
  {
   temp=p->next;
   printf("\nInput a wrong char!Input again:\n");
   for(;;)
   {    
    if (temp!=NULL)
     printf("%c",temp->char_ch);      
    else
     break;
    temp=temp->next;
   }
  }
 }while(ch!='#');/*输入待比较字符串，以'#'结束*/
 p=p->next;
 h=p;
 dosome();/*开始识别*/
 if(right)
  printf("\nOK!\n");
 else
  printf("\nError!\n");
 getch();
}