C++. Calculator. Usage of namespace and switch statements.

calculator.cpp

#include <iostream>

using std::cin;
using std::cout;
using std::endl;

// Define a top-level namespace for the calculator
namespace calculator {
  // Define a nested namespace for the functions
  namespace functions {
    char operand;
    double num1;
    double num2;
    double result;
    bool valid; // a flag to indicate if the operand is valid

    void getUserInput()
    {
      cout << "Enter an operand: ";
      cin >> operand;
      if(!valid) {
        cout << "Invalid operand: " << operand << endl;
        return;
      }
      cout << "Enter first number: ";
      cin >> num1;
      cout << "Enter second number: ";
      cin >> num2;
    }

    void calculate()
    {
      valid = true; // assume the operand is valid by default
      switch (operand) {
      case '+':
        result = num1 + num2;
        break;
      case '-':
        result = num1 - num2;
        break;
      case '/':
        result = num1 / num2;
        break;
      case '*':
        result = num1 * num2;
        break;
      case '%':
        result = (int)num1 % (int)num2;
        break;
      default:
        valid = false; // set the flag to false if the operand is invalid
        break;
      }
    }

    void printResults()
    {
      if (!valid) { // only print the results if the operand is valid
        cout << "Result: Use a supported operand (* / % + -) " << operand << " cannot be used." << endl;
        return;
      }
      cout << "Performing " << num1 << " " << operand << " " << num2 << endl;
        cout << "Result: " << result << endl;
    }
  }
}

int main(int argc, char const *argv[])
{
  // Call the functions from the nested namespace
  calculator::functions::getUserInput();
  calculator::functions::calculate();
  calculator::functions::printResults();
  return 0;
}