Data Structure and Algorithm

/*******************************************************
 APPLICATION : Evaluation of Postfix Expression
 CODED BY    : Ankit Pokhrel
 COMPILED ON : Borland C++ Ver 5.02
 DATE     : 2010 - June - 10
********************************************************/

#include "iostream.h"
#include "conio.h"
#include "stdio.h"
#include "math.h"

/*********** Class to Represent Stack ************/
template "class T"
class stack
{
 private:
  T *arr;
   int TOP,MAXSTK;

 public:
  stack()
   {
    MAXSTK = 31;
    arr = new T[MAXSTK];
    TOP = 0;
   }

   stack(int n)
   {
    MAXSTK = n + 1;
    arr = new T[MAXSTK];
    TOP = 0;
   }

   friend void push(stack &,T); //Push an Item to Stack
   friend T pop(stack &); //Pop an Item From Stack
   friend int empty(stack); //To Check wheter the stack is empty or not
~stack()
   {
    delete arr; //Destroy arr
   }
};

template "class T"
void push(stack "T" &s, T item)
{
 if(s.TOP != s.MAXSTK)
  {
    s.TOP += 1;
    s.arr[s.TOP] = item;
   }

 else //Overflow Condition
cout << "\nStack Overflow.";
}

template "class T"
T pop(stack "T" &s)
{
 T temp;
 if(s.TOP != 0)
  {
  temp = s.arr[s.TOP];
    s.TOP -= 1;
    return temp;
   }

 else //Underflow Condition
  {
   temp = -999;
   return temp;
  }
}

template "class T"
int empty(stack "T" s)
{
 if(s.TOP == 0) //Stack is empty
  return 1;

 else
  return 0;
}

int main()
{
 char postfix[30],temp[8];
 int i = 0;
 cout << "Enter a Valid Postfix Expression,\n";
 cout << "Write Expression in One Line Seperated by Space,\n";
 cout << "Hit Enter when Finished\n\n";
 postfix[i - 1] = '\0';
 while(postfix[i-1] != '\n') //Until a user hit Enter key
  postfix[i++] = getchar(); //Get a Character

 stack "float" stk(50); //Float Stack
 float value,operand1,operand2,item;

 i = 0;
 int j,pos = 0,k;
 while(postfix[i-1] != '\n')
  {
    if(postfix[i] >= '0' && postfix[i] <= '9') //If Number is found
     {
       temp[0] = postfix[i]; // Save Postfix[i] to temp
       j = i+1;
       k = 1;
       if(postfix[i+1] != ' ') //Check for next character, If not Space
        {
         while(postfix[j] != ' ') //While space is not found
         temp[k++] = postfix[j++]; //Save Postfix[j] to temp
        }
       temp[k] = '\0'; //End String temp
       pos = j + 1; //Update position
       item = atof(temp); //Convert string temp to float and store to item
       push(stk,item); //Push to stack
      }

    else if(postfix[i] == '+' || postfix[i] == '-' || postfix[i] == '*' || postfix[i] == '/' || postfix[i] == '$' || postfix[i] == ' ') //If Operator is found
     {
        operand2 = pop(stk); //Pop operand2 from Stack
        if(operand2 == -999) //if Underflow Condition
         break; //break from loop
        operand1 = pop(stk); //Pop operand1 from Stack
        if(operand1 == -999)
         break;

        if(postfix[i] == '+')
       value = operand1 + operand2;

        if(postfix[i] == '-')
       value = operand1 - operand2;

        if(postfix[i] == '*')
       value = operand1 * operand2;

        if(postfix[i] == '/')
       if(operand2 != 0)
       value = operand1 / float(operand2);
          else
           {
            cout << "\nError ! Cannot Divide by Zero";
            getch();
            return 0;
           }

        if(postfix[i] == '$') //Power
       value = pow(operand1,operand2);

       push(stk,value); //Push result to stack
       pos += 2; //Update position
    }

   else
    {
     cout << "\nError : Illegal Character";
     getch();
     return 0;
    }

   i = pos; //Update i
  }

 float Result = pop(stk); //Pop Result
 if(Result == -999 || !empty(stk))//If Underflow Condition or stack is not empty, Print Error message and exit
  {
  cout << "\nError : The Given Postfix Expression is Not Valid.";
  getch();
   return 0;
  }

 else //Print Result
  cout << "\nResult = " << Result;

 getch();
 return 0;
}