RPN using Linked Lists - c++

Question

I am having trouble figuring out an RPN calculator where we have to use Linked List for this assignment. ( I had finished the assignment using the stack<double> method, but It HAS to be using linked lists.
I am having some trouble with the Error checking:
Too many operators (+ - / *)
Too many operands (doubles)
Division by zero
The program is supposed to continue to take and evaluate expressions until the user enters a zero (0) on a line by itself followed by a new line. I am also having some trouble with this. Since I put in my error checking for "too many operands", it
WILL NOT ALLOW ME TO DO A SECOND CALCULATAION , OUTPUT WILL BE "TOO MANY OPERANDS"
I can't seem to get an error check to work for "Too many operators"
I have tried several different things for the required error checking and looked at many other RPN questions on different sites, as you can see through some of the things I tried and commented out.
Any help would be greatly appreciated!
Thanks
#include <iostream>
#include <string>
#include <sstream>
#include <iomanip>
using namespace std;
struct NODE
{
float num;
NODE *next;
};
class stack
{
private:
NODE *head;
public:
stack();
void push(float);
float pop();
int nElements();
float display();
};
class RPN: public stack
{
public:
void add();
void subtract();
void multiply();
void divide();
};
stack::stack()
{
head = NULL;
}
void stack::push(float a_number)
{
NODE *temp = new NODE;
if (temp)
{
temp->num = a_number;
temp->next = head;
head = temp;
}
}
float stack::pop()
{
float number = 0;
if (!head)
{
return 0;
}
else
{
NODE *temp = head;
number = head->num;
head = temp->next;
delete temp;
}
return number;
}
int stack::nElements()
{
int counter=0;
for (NODE *node = head; node; node=node->next)
{
counter++;
}
return counter;
}
float stack::display()
{
//ERROR CHECKING TOO MANY OPERANDS??? PRINTING TOO MANY OPERANDS FOR : 100 10 50 25 / * - -2 / = , but still giving correct output && WILL NOT ALLOW ME TO DO A SECOND CALCULATAION , OUTPUT WILL BE TOO MANY OPERANDS
if(nElements() !=1)
{
cout << "Error: too many operands" << endl;
return 1;
}
/*
// if( nElements() < 2 )
{
cout << "Error: too many operators" << endl;
return 1;
}
*/
else //(nElements() > 0)
{
float temp = pop();
cout << temp << endl;
push(temp);
return temp;
}
}
void RPN::add()
{
if (nElements()>=2)
{
push(pop() + pop());
}
}
void RPN::subtract()
{
if (nElements()>=2)
{
push(0 - pop() + pop());
}
}
void RPN::multiply()
{
if (nElements()>=2)
{
push(pop() * pop());
}
}
int RPN::divide()
{
double op2;
op2 = pop();
if(op2 != 0.0)
{
push(pop() / op2);
}
else
{
cout << "Error: Division by zero.\n"; //??? Still printing output
return -1;
}
}
//Function prototype for isOperator
bool isOperator(const string& input);
//Function prototype for perforOperation
int performOperation(const string& input, RPN& calculator);
Int main(){
RPN calculator;
string input;
float num;
cout << "RPN Calculator: " << endl;
cout << "Input\n";
while(input != "0")
{
//Terminate program when 0 is entered by user
while(true)
{
// get input
cin >> input;
// check for being numeric value
if(istringstream(input) >> num)
{
//use push function
calculator.push(num);
}
// check for operator
else if(isOperator(input))
{
performOperation(input, calculator);
}
// If user enters 0 on a line followed by a new line, the program exits ????????????
else if(input == "0\n")
{
return -1;
}
}
}
}
bool isOperator(const string& input)
{
static const string operators ="-+*/";
if (input.length() == 1) // right size to be an operator.
{
return operators.find_first_of(input[0]) != string::npos;
// look in the operator string for the first (and only) character in input
}
return false;
}
int performOperation(const string& input, RPN& calculator)
{
//double firstOperand = 0;
//double secondOperand = 0;
//double result;
/*
if( calculator.size() > 2 ) //Error check gives a false error for last input ???
{
cout << "Error: too many operands" << endl;
return 1;
}
//Error chceck for too many operators ////STILL PRINT OUTPUT???
if( calculator.size() < 2 )
{
cout << "Error: too many operators" << endl;
return 1;
}
*/
switch (input[0])
{
case '+': calculator.add();
calculator.display();
break;
case '-': calculator.subtract();
calculator.display();
break;
case '*': calculator.multiply();
calculator.display();
break;
case '/': calculator.divide();
//if (firstOperand / 0)
//{
// cout << "Error: Divide by 0.\n";
//}
calculator.display();
break;
}
/*
if (secondOperand == 0)
{ // moved this test to here because it's the only place it matters.
cout << "Error: Division by 0.\n";
return -1;
}
*/
return 0;
}
This is the sample input and output
Input Output
10 15 + = 25
10 15 - = -5
2.5 3.5 + = 6 (or 6.0)
10 0 / = Error: Division by zero
10 20 * / = Error: Too many operators
12 20 30 / = Error: Too many operands
-10 -30 - = 20
100 10 50 25 / * - -2 / = -40
I got the error division by 0 check to work, It just keeps printing the output in addition to the error...How could I fix this?
int RPN::divide()
{
double op2;
op2 = pop();
if(op2 != 0.0)
{
push(pop() / op2);
}
else
{
cout << "Error: Division by zero.\n";
return -1;
}
}

Answer 1

The problem is that you always leave the result of the calculation on the stack. So when you do the second calculation you aren't starting with an empty stack. Simple fix is to delete this line in stack::display()
push(temp);
Probably should rename stack::display() to stack::display_and_pop() as well.