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Are you interested in learning how to build a powerful calculator using C++? Look no further! In this article, we’ll show you how to create a stack-based calculator that can perform complex arithmetic operations with ease. By using postfix notation, also known as Reverse Polish Notation (RPN), and the stack data structure, we’ll demonstrate how to efficiently evaluate mathematical expressions. Get ready to become a programming pro!


Stacks are a fundamental concept in computer science and are widely used in many different applications. Essentially, a stack is a container that follows the “Last In, First Out” principle, meaning that the last element added to the stack will be the first one to be removed. This makes it a simple yet powerful tool for managing data, especially in expressions and algorithms. With the ability to efficiently add and remove elements, stacks have become a popular choice for many programmers and developers, and are an essential part of any programmer’s toolkit.


Ready to build a calculator? The first step is to create a cool class called stackCalculator. This class is essential as it will handle the evaluation of postfix expressions. It does this by using a stack to store operands and perform operations. With the stackCalculator you'll be able to masterfully crunch numbers with ease!

#include <iostream>
#include <stack>
#include <sstream>

class StackCalculator {
  double calculate(const std::string& expression) {
   // Implementation goes here

 std::stack<double> operandStack;

 // Helper functions go here

Let’s tackle this postfix expression head-on! We need to dissect this baby and figure out which parts are digits and which parts are operators. Luckily, we’ve got a secret weapon: std::istringstream. With its help, we'll be able to easily tokenize the expression and determine whether each token is a number or an operator. So, let's rev up our engines and get ready to calculate!

bool isNumber(const std::string& str) {
  return !str.empty() && str.find_first_not_of("0123456789.") == std::string::npos;

bool isOperator(const std::string& str) {
 return str == "+" || str == "-" || str == "*" || str == "/";

Now it's time to get to the heart of our calculator: evaluating the postfix expression. We'll start by looping through the tokens we extracted from the input expression. If we come across a number, we'll add it to our stack of operands. But if we see an operator, things get a little more interesting! We'll need to perform the relevant operation on the top two operands from the stack, and then push the resulting value back onto the stack. By doing this repeatedly until we've gone through all the tokens, we'll be able to calculate the final value of the expression. Let's get to it!

double performOperation(double operand1, double operand2,
  const std::string & op) {
  if (op == "+") 
    return operand1 + operand2;
  else if (op == "-") 
    return operand1– operand2;
  else if (op == "*") 
    return operand1 * operand2;
  else if (op == "/") 
    if (operand2 == 0) 
      throw std::runtime_error("Division by zero.");

    return operand1 / operand2;
  throw std::runtime_error("Invalid operator.");

double calculate(const std::string & expression) {
  std::istringstream iss(expression);
  std::string token;
  while (iss >> token) {
    if (isNumber(token)) {
      double number = std::stod(token);
    } else if (isOperator(token)) {
      if (operandStack.size() < 2) 
        throw std::runtime_error("Invalid expression.");
      else {
        double operand2 =;
        double operand1 =;
        double result = performOperation(operand1, operand2, token);
    } else 
      throw std::runtime_error("Invalid token in expression.");

  if (operandStack.size() != 1) 
    throw std::runtime_error("Invalid expression.");


Our calculator should handle various scenarios like division by zero or invalid expressions. We’ll include appropriate error handling to provide meaningful feedback to users.


The Stack-based calculator in C++ is a well-designed and efficient tool for evaluating postfix expressions. By using a stack data structure, it simplifies the evaluation algorithm and eliminates the need for parentheses and operator precedence rules. This calculator can perform basic arithmetic operations, negative numbers, and decimal points. It also has the potential for more complex operations and functions, such as exponentiation, square roots, and trigonometric functions. Its simplicity and efficiency make it a great starting point for more advanced mathematical calculations. Overall, the calculator is a valuable tool for anyone performing mathematical calculations and looking for a reliable and efficient solution.


Here is the GitHub link where you can find the complete implementation of the stack-based calculator.

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