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4_EXPRESSIONTREE.cpp
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4_EXPRESSIONTREE.cpp
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//
// Created by piyush on 4/4/19.
//
#include<bits/stdc++.h>
using namespace std;
struct node
{
char optr;
node *l;
node *r;
};
class stack1
{
public :
node *stck[20], *m;
int top;
stack1()
{
top = -1;
}
void push(node *p)
{
++top;
stck[top] = p;
}
bool isstackempty()
{
if(top == -1)
return true;
else
return false;
}
bool isstackfull()
{
if(top == 20)
return true;
else
return false;
}
node* pop()
{
return stck[top--];
}
node* gettop()
{
if(!isstackempty())
return stck[top];
else
return NULL;
}
};
class exptree
{
public :
char exp[20];
int priority(char ch);
void getExpression();
void createxptree();
stack1 operand,optor; //this stacks are for computing in creation of expression tree
stack1 s1,s2; //this stacks are for postorder traversal
node *root;
void pos_dis(node *t); //recursive fuction for postorder traversal
void pos_dis_nonrec(); //non-recursive function for postorder traversal
};
void exptree :: getExpression()
{
cout << "\n Enter the expression : ";
cin >> exp;
}
int exptree :: priority(char ch)
{
switch(ch)
{
case '-' :
return 1;
case '+' :
return 1;
case '*' :
return 2;
case '/' :
return 2;
}
}
void exptree :: createxptree()
{
node *nn, *temp;
for(int i = 0; exp[i] != '\0'; i++)
{
nn = new node;
nn->l = NULL;
nn->r = NULL;
nn->optr = exp[i];
if(nn->optr == '+' || nn->optr == '-' || nn-> optr == '*' || nn->optr == '/')
{
if(optor.isstackempty())
{
optor.push(nn);
}
else
{
if(priority((optor.gettop())->optr) >= priority(nn->optr))
{
temp = optor.pop();
temp->r = operand.pop();
temp->l = operand.pop();
operand.push(temp);
optor.push(nn);
}
else
{
optor.push(nn);
}
}
}
else
{
operand.push(nn);
}
}
while(!optor.isstackempty())
{
node *t = optor.pop();
t->r = operand.pop();
t->l = operand.pop();
operand.push(t);
}
root = operand.gettop();
//cout << root->r << endl;
}
void exptree :: pos_dis(node *t)
{
if(t != NULL)
{
pos_dis(t->l);
pos_dis(t->r);
cout << t->optr << " ";
}
}
void exptree ::pos_dis_nonrec() {
//s1 stack is for computing and s2 stack is our display stack
node *tptr;
tptr = root; //root contains address of very first node address
do{
//traversing to very right node of tree
while(tptr != NULL){
s1.push(tptr);
s2.push(tptr);
tptr = tptr->r;
}
tptr = s1.pop();
//finding the node which has left child
while(!s1.isstackempty() && tptr->l == NULL){
tptr = s1.pop();
}
//after getting node who is having left child point to that left child
tptr = tptr->l;
//and again repeat the same procedure till the stack1 gets empty or nodes are over
}while(!s1.isstackempty() || tptr != NULL);
//printing the output stack
cout << "\nPostfix Expression : ";
do{
tptr = s2.pop();
cout << tptr->optr << " ";
}while(!s2.isstackempty());
}
int main()
{
exptree exp1;
int sw,dw;
do{
dw = 1;
cout << "\n(1). To get infix expression ";
cout << "\n(2). To display postfix expression ";
cout << "\n(3). To Exit";
cin >> sw;
switch(sw){
case 1:
exp1.getExpression();
exp1.createxptree();
break;
case 2:
exp1.pos_dis_nonrec();
//exp1.pos_dis(exp1.root);
break;
case 3:
dw = 0;
break;
default:
cout << "\nInvalid Input!!!";
}
}while(dw);
return 0;
}