===Headfile===
//
// Created by Alexander Dietrich on 09.03.2017.
//

#ifndef POSTFIX_STACK_H
#define POSTFIX_STACK_H

#include <iostream>

class Node{
public:
    Node* getNext(){
        return next;
    }
    int getValue(){
        return value;
    }

    void setNext(Node* nextNext){
        next = nextNext;
    }
    void setValue(int number){
        value = number;
    }

private:
    Node *next;
    int value;
};


class Stack{
public:
    Stack(); //constructor
    ~Stack(); //destructor

    void push(int value);
    int pop();

private:
    Node *first;
};

#endif //POSTFIX_STACK_H


======stack.cpp======
//
// Created by Alexander Dietrich on 09.03.2017.
//
#include "stack.h"

Stack::Stack() {
    // stack wird auf auf null gesetzt
    first = nullptr;
}

Stack::~Stack() {
    // destructor -> stack wird wieder gelöscht (allocated mem freigegeben)
    Node* current = first;
    while(current != nullptr){
        Node* tempNext = current->getNext();
        delete current;
        current = tempNext;
    }
}

void Stack::push(int value) {
    // nächste Eingabe wird auf den Stack gelagert
    if(first == nullptr){
        first = new Node();
        first->setValue(value);
        first->setNext(nullptr);
    }else{
        Node *tmp = new Node();
        tmp->setNext(first);
        tmp->setValue(value);
        first = tmp;
    }
}

int Stack::pop() {
    // die zuletzt eingegebene Zahl wir zurückgegeben vom Stack
    int toReturn = first->getValue();
    Node *next = first->getNext();

    delete first;

    first = next;

    return toReturn;
}

==============main.c==============
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include "stack.h"

using namespace std;

int main() {
    int number1 = 0, number2 = 0, end = 1;

    Stack* liste = new Stack();


    while(end == 1) {
        std::string eingabe = "";
        std::cin >> eingabe;


        if (eingabe.compare("-") == 0) {
            number2 = liste->pop();
            number1 = liste->pop();
            liste->push(number1 - number2);
        } else if (eingabe.compare("+") == 0) {
            number2 = liste->pop();
            number1 = liste->pop();
            liste->push(number1 + number2);
        } else if (eingabe.compare("/") == 0) {
            number2 = liste->pop();
            number1 = liste->pop();
            liste->push(number1 / number2);
        } else if (eingabe.compare("%") == 0) {
            number2 = liste->pop();
            number1 = liste->pop();
            liste->push(number1 % number2);
        } else if (eingabe.compare("*") == 0) {
            number2 = liste->pop();
            number1 = liste->pop();
            liste->push(number1 * number2);
        } else if (eingabe.compare("=") == 0) {
            number1 = liste->pop();
            cout << number1 << endl;
            end = 0;
        } else {
            std::stringstream s(eingabe);
            s >> number1;
            liste->push(number1);
        }
    }

	delete liste;
    return 0;
}