Expression Tree (using BST)

/*For given expression eg. a-b*c-d/e+f construct inorder sequence and traverse 

it using postorder traversal(non recursive).*/

#include<iostream>
#include<string>

using namespace std;
typedef struct node
{
char cData;

class Cstack
struct node  *pRt,*pLf;
}NODE;
{
 NODE *pS[20];

void fPush(NODE* pPtr)
int iTop;
public:
 Cstack()
    {
  iTop=-1;
    }
 {

pTmp=pS[iTop];
iTop++;
  pS[iTop]=pPtr;
 }
 NODE* fPop()
 {
 NODE *pTmp;

return(pS[iTop]);
iTop--;
 return(pTmp);
 }
 NODE* fTop()
 {
 }
 int fIsempty()
 {

string sExpr;
if(iTop==-1)
   return 1;
   return 0;
 }
};
class Cexp
{
Cstack oS1,oS2;

void fDisplayPos(NODE*);
int iLen;
public:
void fGetExp();
int fPriority(char);
NODE* fBuildTree();

cout<<"Enter Expression : ";
void fDisplay(NODE*,int,NODE*);
};
void Cexp::fGetExp()
{

 cin>>sExpr;
 iLen=sExpr.size();

}

if(sExpr[i]!='*'&&sExpr[i]!='/'&&sExpr[i]!='+'&&sExpr[i]!='-')
NODE* Cexp::fBuildTree()
{
 NODE *pNn,*pOpr,*pOp1,*pOp2;

 for(int i=iLen-1;i>=0;i--)
 {
  {
  pNn=new NODE;

if(!oS2.fIsempty()&&(fPriority((oS2.fTop())->cData)>fPriority(sExpr[i])))
pNn->cData=sExpr[i];
  pNn->pLf=pNn->pRt=NULL;
  oS1.fPush(pNn);
  }
  else
  {
   {

pOp1=oS1.fPop();
while(  fPriority((oS2.fTop())->cData)>fPriority(sExpr[i])  )
    {
    pOpr=oS2.fPop();
    pOp2=oS1.fPop();
    pOpr->pRt=pOp1;

while(!oS2.fIsempty())
pOpr->pLf=pOp2;
    oS1.fPush(pOpr);
    }
         }
   pNn=new NODE;
   pNn->cData=sExpr[i];
   pNn->pRt=pNn->pLf=NULL;
   oS2.fPush(pNn);
  }
 }
{

int Cexp::fPriority(char cCh)
pOpr=oS2.fPop();
    pOp2=oS1.fPop();
    pOp1=oS1.fPop();
    pOpr->pRt=pOp1;
    pOpr->pLf=pOp2;
    oS1.fPush(pOpr);
}

return oS1.fTop();

}
{
 if(cCh=='+'||cCh=='-')

oS2.fPush(pTmp);
return 1;
 else
  return 2;
}
void Cexp::fDisplayPos(NODE *pRoot)
{
Cstack oS1,oS2;
NODE *pTmp;
oS1.fPush(pRoot);
while(!oS1.fIsempty())
{
pTmp=oS1.fTop();
oS1.fPop();
if(pTmp->pLf)

void Cexp::fDisplay(NODE *ptr, int level,NODE *pRoot)
oS1.fPush(pTmp->pLf);
if(pTmp->pRt)
oS1.fPush(pTmp->pRt);
}
while(!oS2.fIsempty())
{
pTmp=oS2.fTop();
oS2.fPop();
cout<<pTmp->cData<<" ";
}
}
{
int i;
if (ptr != NULL)
{
fDisplay(ptr->pRt, level+1,pRoot);

pRoot=o.fBuildTree();
cout<<endl;
if (ptr == pRoot)
cout<<"Root->:  ";
else
{
for (i = 0;i < level;i++)
cout<<"       ";
}
cout<<ptr->cData;
fDisplay(ptr->pLf, level+1,pRoot);
}
}
int main()
{
NODE *pRoot;
Cexp o;
o.fGetExp();

o.fDisplay(pRoot,1,pRoot);
cout<<"\n";
o.fDisplayPos(pRoot);
cout<<"\n";

return 0;


}