The program is about infix_to_postfix conversation and postfix evaluation using

Question

The program is about infix_to_postfix conversation and postfix evaluation using one class (Expression).

I have this class:

#ifndef EXPRESSION_H

#define EXPRESSION_H

#include <iostream>

#include <string>

#include <sstream>

#include <cctype>

#include "expression_exception.h"

using namespace std;

class Expression {

friend ostream &operator <<(ostream &os, const Expression &exp);

public:

Expression(string infix);

double evaluate();

string getInfix();

string getPostfix();

private:

void compile();

double evaluate(char optr, double operand1, double operand2);

int Expression::precLevel(char optr);

int Expression::isLeftAssociative(char optr);

string infix;

string postfix;

};

#endif

Then I have:

#ifndef EXPRESSION_EXCEPTION_H

#define EXPRESSION_EXCEPTION_H

#include <string>

class ExpressionException {

public:

ExpressionException(std::string message) : message(message) {}

std::string getMessage() {return "*** ExpressionException: " + message;}

private:

std::string message;

};

#endif

This is how I will use my class:

#include <iostream>

#include <string>

#include <sstream>

#include <cctype>

#include "expression.h"

#include "expression_exception.h"

using namespace std;

main() {

string infix;

cout << "Enter an infix expression: ";

while (getline(cin, infix)) {

try {

Expression exp = infix;

cout << exp.evaluate() << endl;

} catch (ExpressionException e) {

cerr << e.getMessage() << endl;

}

cout << "Enter a infix expression: ";

}

}

I badly need help to make it all work together.

Explanation / Answer

# include # include # include # include struct node { char data; node *next; }; node *top=NULL; node *bottom=NULL; node *entry; node *last_entry; node *second_last_entry; void push(constchar); constchar pop( ); void infix_to_postfix(constchar *); int main( ) { clrscr( ); char Infix_expression[100]={NULL}; coutInfix_expression; infix_to_postfix(Infix_expression); getch( ); return 0; } /*************************************************************************///----------------------------- push(const char) ----------------------///*************************************************************************/void push(constchar Symbol) { entry=new node; if(bottom==NULL) { entry->data=Symbol; entry->next=NULL; bottom=entry; top=entry; } else { entry->data=Symbol; entry->next=NULL; top->next=entry; top=entry; } } /*************************************************************************///-------------------------------- pop( ) -----------------------------///*************************************************************************/constchar pop( ) { char Symbol=NULL; if(bottom==NULL) coutnext=NULL; } return Symbol; } /*************************************************************************///--------------------- infix_to_postfix(const char *) ----------------///*************************************************************************/void infix_to_postfix(constchar *Infix) { char Infix_expression[100]={NULL}; char Postfix_expression[100]={NULL}; strcpy(Infix_expression,"("); strcat(Infix_expression,Infix); strcat(Infix_expression,")"); char Symbol[5]={NULL}; char Temp[5]={NULL}; for(int count=0;count

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