How to sum all the items in stack? Postfix calculator

Question

I'm making a postfix calculator and I want to make a new feature to it. How can I sum all the items in a stack and then delete the items used for summing from the stack and then push the sum back to the stack? All this should happen by pressing command 's'.

I tried doing it like this but it always prints me just 0.

    case 's':
        if (numbers.top().first == underflow)
            cout << "Stack empty" << endl;
        else {
            numbers.pop();
            if (numbers.top().first == underflow) {
                cout << "Stack has just one entry" << endl;
                numbers.push(p);
            }

            else {
                while (!numbers.empty()) {
                    sum += numbers.top().second;

                }
                numbers.push(sum);
                cout << sum << endl;

            }
        }
        break;

Here is some code of my main.cpp.

#include <iostream>
#include "Stack.h"
#include <cmath>
using namespace std;

void help()
{
    cout
        << "[?]push to stack [=]print top [x]exchange [s]sum [a]average" << endl
        << "[+] [-] [*] [/] [%] [^] [v] are arithmetic operations" << endl
        << "[Q]uit." << endl;
}

char get_command()
{
    char command;
    bool waiting = true;
    cout 
        << "Select command and press <Enter>:" << endl;

    while (waiting) {
        cin >> command;
        command = tolower(command);
        if (command == '?' || command == '=' || command == '+' ||
            command == '-' || command == '*' || command == '/' ||
            command == 'q' || command == 'x' || command == 's' || 
            command == 'a' || command == '%' || command == '^' || 
            command == 'v') waiting = false;


        else {
            cout << "Please enter a valid command:" << endl;
        }
    }
    return command;
}


bool do_command(char command, Stack& numbers)

{
    double p, q, g, r;
    double sum = 0;
    switch (command) {
    case '?':
        cout << "Enter a real number: " << flush;
        cin >> p;
        if (numbers.push(p) == overflow)
            cout << "Warning: Stack full, lost number" << endl;
        break;

    case '=':
        if (numbers.top().first == underflow)
            cout << "Stack empty" << endl;
        else
            cout << p << endl;
        break;

    case '+':
        if (numbers.top().first == underflow)
            cout << "Stack empty" << endl;
        else {
            numbers.pop();
            if (numbers.top().first == underflow) {
                cout << "Stack has just one entry" << endl;
                numbers.push(p);
            }

            else {
                numbers.pop();
                if (numbers.push(q + p) == overflow)
                    cout << "Warning: Stack full, lost result" << endl;
            }
        }
        break;

    case '-':
        if (numbers.top().first == underflow)
            cout << "Stack empty" << endl;
        else {
            numbers.pop();
            if (numbers.top().first == underflow) {
                cout << "Stack has just one entry" << endl;
                numbers.push(p);
            }

            else {
                numbers.pop();
                if (numbers.push(q - p) == overflow)
                    cout << "Warning: Stack full, lost result" << endl;
            }
        }
        break;

    case '*':
        if (numbers.top().first == underflow)
            cout << "Stack empty" << endl;
        else {
            numbers.pop();
            if (numbers.top().first == underflow) {
                cout << "Stack has just one entry" << endl;
                numbers.push(p);
            }

            else {
                numbers.pop();
                if (numbers.push(q * p) == overflow)
                    cout << "Warning: Stack full, lost result" << endl;
            }
        }
        break;

    case '/':
        if (numbers.top().first == underflow)
            cout << "Stack empty" << endl;
        else {
            numbers.pop();
            if (numbers.top().first == underflow) {
                cout << "Stack has just one entry" << endl;
                numbers.push(p);
            }

            else {
                numbers.pop();
                if (numbers.push(q / p) == overflow)
                    cout << "Warning: Stack full, lost result" << endl;
            }
        }
        break;

    case 'x':
        if (numbers.top().first == underflow)
            cout << "Stack empty" << endl;
        else {
            numbers.pop();
            if (numbers.top().first == underflow) {
                cout << "Stack has just one entry" << endl;
                numbers.push(p);
            }

            else {
                numbers.pop();
                numbers.pop();
                numbers.push(p);
                numbers.push(q);
            }
        }
        break;

    case 's':
        if (numbers.top().first == underflow)
            cout << "Stack empty" << endl;
        else {
            numbers.pop();
            if (numbers.top().first == underflow) {
                cout << "Stack has just one entry" << endl;
                numbers.push(p);
            }

            else {
                while (!numbers.empty()) {
                    sum += numbers.top().second;

                }
                numbers.push(sum);
                cout << sum << endl;

            }
        }
        break;

Here is my Stack.cpp.

Error_code Stack::push(const Stack_entry& item)
/*
Pre:  None.
Post: If the Stack is not full, item is added to the top
      of the Stack.  If the Stack is full,
      an Error_code of overflow is returned and the Stack is left unchanged.
*/

{
    Error_code outcome = success;
    if (count >= maxstack)
        outcome = overflow;
    else
        entry[count++] = item;
    return outcome;
}


Error_code Stack::pop()
/*
Pre:  None.
Post: If the Stack is not empty, the top of
      the Stack is removed.  If the Stack
      is empty, an Error_code of underflow is returned.
*/

{
    Error_code outcome = success;
    if (count == 0)
        outcome = underflow;
    else --count;
    return outcome;
}


pair<Error_code, int> Stack::top() const
{
    pair<Error_code, int> p;
    Error_code outcome = success;
    if (count == 0) 
        p.first = underflow;
        p.second = 0;
        return p;

    p.first = outcome;
    p.second = entry[count - 1];
    return p;
}

Here is my Stack.h

#include "Utility.h"

typedef double Stack_entry;

const int maxstack = 10;

class Stack {
public:
    Stack();
    bool empty() const;
    Error_code pop();
    //Error_code top(Stack_entry& item) const;
    Error_code push(const Stack_entry& item);
    //Error_code pop_top(Stack& s, Stack_entry& item);
    double size() const; 
    std::pair<Error_code, int> top() const;

private:
    int count;
    Stack_entry entry[maxstack];
};

I would expect it to sum all the numbers in the stack together and then deleting them and then pushing it back to the stack. I would really appreciate any help. Thanks in advance.

Answer 1

pop doesn't return value like other languages in C++. You need to use top function for returning top element in stack. You can add that element to sum, then remove it with pop. You can implement it as below:

while (!numbers.empty()) 
{
    sum += numbers.top();
    numbers.pop()
}

For Op's another request:

Change top's implementation to this:

std::pair<Error_code,int> top() const
    {
        std::pair<Error_code,int> p;
        Error_code outcome = success;
        if (count == 0)
            p.first = underflow;
            p.second = 0;
            return p;

        p.first = outcome;
        p.second = entry[count -1];
        return p;
    }

And your first problem's solution becomes this:

while (!numbers.empty()) 
    {
        sum += numbers.top().second;
        numbers.pop()
    }

if you want outcome you can do numbers.top().first. That's all.