String handling using Boost's tokenizer

simple_calc.cpp

#define CATCH_CONFIG_MAIN
#include "catch.hpp"
#include <boost/tokenizer.hpp>
#include <iostream>

using namespace std::literals::string_literals;

int basic_calc(const std::string &input) {

  boost::char_separator<char> operators{"+-*/"};
  boost::tokenizer<boost::char_separator<char>> tokens{input, operators};

  auto itr = tokens.begin();

  auto operand1 = *itr++;
  auto operand2 = *itr;
  char operation = input[operand1.length()];

  std::cout << "[T]" << operand1 << " " << input[operand1.length()] << " "
            << operand2 << std::endl;
  int result{};

  switch (operation) {
  case '+':
    result = stoi(operand1) + stoi(operand2);
    break;
  case '-':
    result = stoi(operand1) - stoi(operand2);
    break;
  case '*':
    result = stoi(operand1) * stoi(operand2);
    break;
  case '/':
    result = stoi(operand1) / stoi(operand2);
    break;
  default:
    std::cout << "No valid operand" << std::endl;
  }

  return result;
}

TEST_CASE("check calculator's functionality") {
  auto str_add = "100+11"s;
  auto str_sub = "100-11"s;

  SECTION("add1") { REQUIRE(basic_calc(str_add) == 111); }
  SECTION("sub1") { REQUIRE(basic_calc(str_sub) == 89); }