Help fix postfix expression pgm

[l3ecl]

My program evaluates a postfix expression. I'm trying to edit my code so that the user does not need to enter the equal sign '=' as part of the input. I have two solutions but am having a very hard time implementing either of them. I can either: input the '=' for the user, or implement an EOF to act as the equal sign. Please help me implement either of these.

below is my code:


//This programm is post fix calculator
#include "stdafx.h"
#include <iostream>
using namespace std;

struct pq {

char st[15];
pq *next;

};

struct es
{
int value;
es* next;

};


bool is_integer(char answer[]);
es *push(es *h, int n);
es *pop_es_head(es *es_head);
pq *pop_pq_head(pq *head);
void printlistpq(struct pq *p);
void printlistes(struct es *e);


int main()
{
pq *head, *current, *temp;
string s;

head = new pq;
cout << "Enter the number and signs"<<endl;
cin >> head->st;

if(head->st[0] != '=')
{
head->next = NULL;
current = head;
temp = new pq;
cin >> temp->st;

while(temp->st[0] != '=')
{
temp->next = NULL;
current->next = temp;
current = current->next;
temp = new pq;
cin >> temp->st;
}
delete temp;
}
printlistpq(head);
es *es_head;
bool integer;
int result;
integer = is_integer(head->st);

if(integer == true)
{
es_head = new es;
es_head->value = atoi(head->st);
es_head->next = NULL;
temp = head->next;
delete head;
head = temp;

while(head != NULL)
{
integer = is_integer(head->st);
if(integer == true)
{
es_head = push(es_head, atoi(head->st));
printlistpq(head);
}
else
{
switch(head->st[0])
{
case '+':
result = es_head->value + es_head->next->value;
printlistpq(head);
es_head = pop_es_head(es_head);
es_head = pop_es_head(es_head);
es_head = push(es_head, result);
break;
case '-':
result = es_head->next->value - es_head->value;
printlistpq(head);
es_head = pop_es_head(es_head);
es_head = pop_es_head(es_head);
es_head = push(es_head, result);
break;
case '*':
result = es_head->value * es_head->next->value;
printlistpq(head);
es_head = pop_es_head(es_head);
es_head = pop_es_head(es_head);
es_head = push(es_head, result);
break;
case '/':
result = es_head->next->value / es_head->value;
printlistpq(head);
es_head = pop_es_head(es_head);
es_head = pop_es_head(es_head);
es_head = push(es_head, result);
break;
default: cout << "Invalid operator.";
}
}
head = pop_pq_head(head);
}

}
printlistpq(head);
if (head == NULL)
{
cout << "The answer is " << es_head->value << ".";
}
system("pause");
return 0;
}



bool is_integer(char answer[]) // checks the input contains non-integer characters.
{
bool integer = true;
int len = int(strlen(answer));

for (int i = 0; i < len; i++)
{
if (answer[i] <= '9' && answer[i] >= '0')
integer = true;
else
{
integer = false;
break;
}
}
return integer;
}



es *push(es *h, int n) // pushes values into the evaluation stack
{
es *temp;
temp = h;
h = new es;
h->value = n;
h->next = temp;
return h;
}


es *pop_es_head(es *es_head) // pops the head of the evaluation stack
{
es *es_temp;
es_temp = es_head->next;
delete es_head;
es_head = es_temp;
return es_head;
}



pq *pop_pq_head(pq *head) // pops the head of the polish queue
{
pq *temp;
temp = head->next;
delete head;
head = temp;
return head;
}

void printlistpq(struct pq *p)
{
struct pq *listptr=p;

cout<<"the polish queue is :\n";
while(listptr!=0)
{
cout<<listptr->st<<endl;
listptr=listptr->next;
}
}

void printlistes(struct es *e)
{
struct es *list=e;

cout<<"the evaluation stack is :\n";
while(list!=0)
{
cout<<list->value<<endl;
list=list->next;
}
}