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To parse a string using Operator Precedence parsing

Posted By: Olivia Campbell     Category: C++ Programming     Views: 9421

To parse a string using Operator Precedence parsing.

Code for To parse a string using Operator Precedence parsing in C++ Programming

#include<iostream.h>
#include<ctype.h>

char ptab[6][6] = {
                    'x', '+', '*', '(', ')', ']',
                    '+', '>', '<', '<', '>', '>',
                    '*', '>', '>', '<', '>', '>',
                    '(', '<', '<', '<', '=', '#',
                    ')', '>', '>', '#', '>', '>',
                    '[', '<', '<', '<', '#', '='
                  };

struct node
{
    char symbol;
    node *lptr;
    node *rptr;
};

struct stack
{
    char sign;
    struct node *optr;
};

char comp(char,char);
void postorder(struct node *);
void preorder(struct node *);
void inorder(struct node *);

void main()
{
       int i=0,tos=0,csf=1;
    char str[15]="[a*b+c]";
    char ans;
    node *x;
    stack s[20];

       s[tos].sign ='[';

       while(str[i]!='\0')
       {
        if(isalpha(str[csf]))
        {
            x=new node;
             x->symbol=str[csf];
             x->lptr=NULL;
             x->rptr=NULL;
            s[tos].optr=x;
        }
        else
        {
            ans=comp(s[tos].sign,str[csf]);
            while(ans=='>')
            {
                 x=new node;
                 x->symbol=s[tos].sign;
                 x->lptr=s[tos-1].optr;
                 x->rptr=s[tos].optr;
                 tos--;
                 s[tos].optr= x;
                ans=comp(s[tos].sign,str[csf]);
            }

            if(ans=='<')
            {
                  tos++;
                  s[tos].sign=str[csf];
            }

            if(ans=='=' && s[tos].sign=='[')
            {
                       break;
            }

            if(s[tos].sign=='(')
            {
                x=s[tos].optr;
                   tos--;
                   s[tos].optr=x;
            }
        }

        csf++;
           i++;
    }

      node *rt=s[0].optr;

      cout<<endl<<"The Postorder of the tree is::";
      postorder(rt);

      cout<<endl<<"The Preorder of the tree is::";
      preorder(rt);

      cout<<endl<<"The Inorder of the tree is::";
      inorder(rt);

    cout<<endl;
}
char comp(char x,char y)
{
       int i=0,j=0;

       while(ptab[i][0]!=x && i<=6)
          i++;

       while(ptab[0][j]!=y &&  j<=6)
         j++;

    return ptab[i][j];
}

void postorder(struct node *rt)
{
    struct node *ptr=rt;
      if(ptr!=NULL)
      {
            postorder(ptr->lptr);
            postorder(ptr->rptr);
            cout<<ptr->symbol;
      }
}

void preorder(struct node *rt)
{
     struct  node *ptr=rt;
    if (ptr!=NULL)
    {
        cout<<ptr->symbol;
        preorder(ptr->lptr);
        preorder(ptr->rptr);
       }
}

void inorder(struct node *rt)
{
     struct   node *ptr=rt;
       if(ptr!=NULL)
       {
        inorder(ptr->lptr);
        cout<<ptr->symbol;
        inorder(ptr->rptr);   
    }
}

/***********************************
OUTPUT
***********************************

The Postorder of the tree is:: ab*c+
The Preorder of the tree is :: +*abc
The Inorder of the tree is :: a*b+c

************************************/
  
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Olivia Campbell
Olivia Campbell author of To parse a string using Operator Precedence parsing is from Toronto, Canada.
 
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