InFix to PostFix and PostFix expression evaluation.

Nice Job

 

I would love to see the programs that changes infix to postfix and then evaluates it in C++ not in C. Could you give it to me or post it or soemthing i am anxious to see it, thanks!

 

Here is what i got i need the main, i want two functions that you did the one that changes infix to post fix and one that evaluates, i am really stuck can you pleaseeee help me!

Here is my .h

Code:

#include <iostream>
using namespace std;

template <typename ElementType>
#ifndef STACK
#define STACK

class Stack
{
   private:
	   class Node
	   {
   public:
   	     ElementType info;
	     Node *next;
	   };
   typedef Node * Nodeptr;

    public:
		Stack();
		Stack(const Stack<ElementType> &);
		~Stack();
		//Stack<ElementType>  operator=(const Stack<ElementType> &);
		bool empty() const; 
		void Push(ElementType item); 
		ElementType Pop(); 
		ElementType Top() const;
		void display(ostream & out) const; 
		
	private: 
		Node *miStack;
};
template <typename ElementType>
ostream & operator<< (ostream & out, const Stack <ElementType> & astack); //ya

#include "stack.template"
#endif 

here is my template (I need something in the top function check it out)

Code:

#include<iostream>
using namespace std;

template <typename ElementType>
Stack<ElementType>::Stack()
{
	miStack=NULL;
}

template <typename ElementType>
Stack<ElementType>::Stack(const Stack<ElementType> & orig)
{
	nodePtr p=orig.miStack;
	nodePtr pnuevo, anterior;
	while (p!=NULL)
	{
		pnuevo=new node;
		pnuevo->info=p->info;
		if (orig.miStack==p)
			miStack=pnuevo;
		else
			anterior->next=pnuevo;
		anterior=pnuevo;
		p=p->next;
	}
	if (orig.miStack==NULL)
		miStack=NULL;
	else
		pnuevo->next=NULL;
}

template <typename ElementType>
Stack<ElementType>::~Stack()
{
	nodePtr p = miStack, anterior;
	while (p!=NULL)
	{
		anterior=p;
		p=p->next;
		delete anterior;
	}
}

/* template <typename ElementType>
Stack<ElementType> Stack<ElementType>::operator = (const Stack<ElementType> & orig)
{
	if (this != & orig)
	{
		nodePtr p=miStack, anterior;
		while (p!=NULL)
		{
			anterior=p;
			p=p->next;
			delete anterior;
		}
	nodePtr q=orig.miStack;
	nodePtr pnuevo;
	while (q!=NULL)
	{
		pnuevo=new node;
		pnuevo->info=p->info;
		if (orig.miStack==p)
			miStack=pnuevo;
		else
			anterior->next=pnuevo;
		anterior=pnuevo;
		q=q->next;
	}
	if (orig.miStack==NULL)
		miStack=NULL;
	else
		miStack=NULL;
}
return *this;
}*/

template <typename ElementType>
bool Stack<ElementType>::empty() const
{
	return (miStack==NULL);
}

template <typename ElementType>
void Stack<ElementType>::Push(ElementType item)
{
	Nodeptr p = new Node;
	p->info=item; 
	p->next=miStack;
	miStack=p;
}

template <typename ElementType>
ElementType Stack<ElementType>::Pop()
{ 
Nodeptr p = miStack, elementType item;
	if(miStack != null)
		item = p->info;
		miStack = miStack->next;
		delete p;
		return item;
	else
	{	cerr<<"Stack vacio.  No se hizo pop "<<endl;
		exit(1);
	}
}

template <typename ElementType>
ElementType Stack<ElementType>::Top()
{ 
	return( )//I dont know what to put here, help me also
}

template <typename ElementType>
void Stack<ElementType>::display (ostream & out)const
{
	nodePtr p;
	p=miStack;
	out<<"Los Elementos de la lista son:";
	while (p!=NULL)
	{
		out<<p->info<<" ";
		p=p->next;
	}
	cout<<endl;
}

template<typename ElementType>	
ostream & operator<<(ostream & out, const Stack<ElementType> & astack)
{  
	astack.display(out); 
	return out;   
}

here is the main(this is what i need help with):

Code:

#include "stack.h"

using namespace std;

void main()
{
	
//HELP!!

}

Please i need help ASAP

 

if i am trying to use more than four variables in postfix expression, output is not coming to me.
for ex: ab+ cd+*
can u guide me
sorry if i am wrong

 

sorry i didn't mentioned clearly, While using postfix evaluation program, if i am typing postfix expression ab+cd+* , result is not coming properly, if ab+ result is ok.
can u verify once. where i am doing wrong

thanks in advance

 

can you make this evaluates a postfix in java....
please cuz i saw it more easier for me to understand it.....
thank you

 

i need a progrm in this....InFix to PostFix and PostFix expression evaluation.....program in c.... i really need ur help..

 

Shabbir,

In the 4th point you mentioed i think it should be operator not operand.

4.If the scanned character is an Operator[not Operand] and the stack is not empty, compare the precedence of the character with the element on top of the stack (topStack). If topStack has higher precedence over the scanned character Pop the stack else Push the scanned character to stack. Repeat this step as long as stack is not empty and topStack has precedence over the character.

May be i am wrong. Please let me konw if i missed something.

 

i try to do this....i want to know if i use this program, is that correct?
Q:
How to write a java program taht evaluates a postfix expression by using concept of stack?
--------------------------------------------

Code:

public class PostfixEval 
{

   public static void main(String[] args) 
    {
      
      TextIO.putln("This program can evaluate postfix expressions such as\n");
      TextIO.putln("        2 2 +");
      TextIO.putln("or");
      TextIO.putln("        7.3 89.2 + 9 1.83 * 2 + /\n");
      TextIO.putln("The operators +, -, *, /, and ^ can be used.\n\n");
      
      while (true) 
        {
             // Get and process one line of input from the user.
        TextIO.putln("\n\n\nEnter a postfix expression or press return to end:\n");
        TextIO.put("? ");
        skipSpaces();
        if (TextIO.peek() == '\n') 
          {
               // If the line is empty (except for spaces), we are done.
            break;
        }
        readAndEvaluate(); // Process the input.
        TextIO.getln(); // Discard the end-of-line.
      }
      
      TextIO.putln("\n\nExiting program.");
      
   } // end main();
   
   
   static void skipSpaces() 
    {
        // Skip past any spaces and tabs on the current input line.
        // When this routine returns, the next character is either
        // the end-of-line character, '\n', or is a non-blank.
      while (TextIO.peek() == ' ' || TextIO.peek() == '\t') 
        {
        TextIO.getAnyChar();
      }
   }
   
   
   static void readAndEvaluate()
     {
        // Read one line of input and process it as a postfix expression.
        // If the input is not a legal postfix expression, then an error
        // message is displayed. Otherwise, the value of the expression
        // is displayed. It is assumed that the first character on
        // the input line is a non-blank. (This is checked in the
        // main() routine.)
       
      NumberStack stack; // For evaluating the expression.
      
      stack = new NumberStack(); // Make a new, empty stack.
      
      TextIO.putln();
      
      while (TextIO.peek() != '\n') 
        {
      
          if ( Character.isDigit(TextIO.peek()) ) 
             {
                  // The next item in input is a number. Read it and
                  // save it on the stack.
              double num = TextIO.getDouble();
              stack.push(num);
              TextIO.putln("   Pushed constant " + num);
          }
          else 
             {
                 // Since the next item is not a number, the only thing
                 // it can legally be is an operator. Get the operator
                 // and perform the operation.
              char op; // The operator, which must be +, -, *, /, or ^.
              double x,y;     // The operands, from the stack, for the operation.
              double answer; // The result, to be pushed onto the stack.
              op = TextIO.getChar();
              if (op != '+' && op != '-' && op != '*' && op != '/' && op != '^') 
                  {
                      // The character is not one of the acceptable operations.
                  TextIO.putln("\nIllegal operator found in input: " + op);
                  return;
              }
              if (stack.isEmpty()) 
                  {
                  TextIO.putln("   Stack is empty while trying to evaluate " + op);
                  TextIO.putln("\nNot enough numbers in expression!");
                  return;
              }
              y = stack.pop();
              if (stack.isEmpty()) 
                  {
                  TextIO.putln("   Stack is empty while trying to evaluate " + op);
                  TextIO.putln("\nNot enough numbers in expression!");
                  return;
              }
              x = stack.pop();
              switch (op) 
                  {
                 case '+': answer = x + y; break;
                 case '-': answer = x - y; break;
                 case '*': answer = x * y; break;
                 case '/': answer = x / y; break;
                 default:   answer = Math.pow(x,y); // (op must be '^'.)
              }
              stack.push(answer);
              TextIO.putln("   Evaluated " + op + " and pushed " + answer);
          }
          
          skipSpaces();
      
      } // end while
      
      // If we get to this point, the input has been read successfully.
      // If the expression was legal, then the value of the expression is
      // on the stack, and it is the only thing on the stack.
      
      if (stack.isEmpty()) 
        { // Impossible if the input is really non-empty.
          TextIO.putln("No expression provided.");
          return;
      }
       
      double value = stack.pop(); // Value of the expression.
      TextIO.putln("   Popped " + value + " at end of expression.");

      if (stack.isEmpty() == false) {
          TextIO.putln("   Stack is not empty.");
          TextIO.putln("\nNot enough operators for all the numbers!");
          return;
      }

      TextIO.putln("\nValue = " + value);
      
      
   } // end readAndEvaluate()


} // end class PostfixEval 

-----------------------------------------------------------------------
Attached the question,i know for you is simple, but i really need your help...Thank you

 

i need some help pls help me...
i have written a code for postfix expression evaluation but what if all the data and expressions to be evaluated are in text file..
pls tell me how can i modify my code ..

Code:

#include <iostream>
#include <stack> 
#include <string>
using namespace std;

void main()
{
    int i, choice = 1;
    string postfixExp;
    char token;
    float value, value1, value2;
    stack<float> s; //Declare a stack of floats

   

    while (choice != 0)
    {
        cout << "1. Evaluate a postfix expression" << endl;
        cout << "0. Exit " << endl;
        cout << "Enter the number for the option: ";

        cin >> choice;
        switch(choice)
        {
            case 1: cout << "Evaluate a postfix expression\n";
                    cout << "Enter the expression: ";
                    cin >> postfixExp;
                    i = 0;
                    token = postfixExp[i];
                    while((i < postfixExp.size()) && (token != '='))
                    {
                        if(isdigit(token))
                        {
                            value = token - '0';
                            s.push(value);
                        }
                        else
                        {
                            value2 = s.top();
                            s.pop();
                            value1 = s.top();
                            s.pop();
                            switch(token)
                            {
                                case '+': value = value1 + value2;
                                          break;
                                case '-': value = value1 - value2;
                                          break;
                                case '*': value = value1*value2;
                                          break;
                                case '/': value = value1/value2;
                                          break;
                            }
                            s.push(value);
                        }
               i++;
               token = postfixExp[i];
                    }
                    value = s.top();
                    s.pop();
                    cout << postfixExp << " " << value << endl;         
                    break;

            case 0: cout << "Exiting the program\n";
                    break;

            default: cout << "Invalid option\n";
                    break;
        }
     cout << endl;
    }
}