postfix_evaluation.cpp

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#include <algorithm>  // for all_of
#include <cassert>    // for assert
#include <iostream>   // for io operations
#include <stack>      // for std::stack
#include <string>     // for stof
#include <vector>     // for std::vector

namespace others {
namespace postfix_expression {

bool is_number(const std::string &s) {
    return !s.empty() && std::all_of(s.begin(), s.end(), ::isdigit);
}

void evaluate(float a, float b, const std::string &operation,
              std::stack<float> &stack) {
    float c = 0;
    const char *op = operation.c_str();
    switch (*op) {
        case '+':
            c = a + b;  // Addition of numbers
            stack.push(c);
            break;
 
        case '-':
            c = a - b;  // Subtraction of numbers
            stack.push(c);
            break;
 
        case '*':
            c = a * b;  // Multiplication of numbers
            stack.push(c);
            break;
 
        case '/':
            c = a / b;  // Division of numbers
            stack.push(c);
            break;
 
        default:
            std::cout << "Operator not defined\n";
            break;
    }
}
 
namespace {
float remove_from_stack(std::stack<float> &stack) {
    if (stack.empty()) {
        throw std::invalid_argument("Not enough operands");
    }
    const auto res = stack.top();
    stack.pop();
    return res;
}
}  // namespace

float postfix_evaluation(const std::vector<std::string> &input) {
    std::stack<float> stack;
 
    for (const auto &scan : input) {
        if (is_number(scan)) {
            stack.push(std::stof(scan));
 
        } else {
            const auto op2 = remove_from_stack(stack);
            const auto op1 = remove_from_stack(stack);
 
            evaluate(op1, op2, scan, stack);
        }
    }
 
    const auto res = remove_from_stack(stack);
    if (!stack.empty()) {
        throw std::invalid_argument("Too many operands");
    }
    return res;
}
}  // namespace postfix_expression
}  // namespace others

static void test_function_1() {
    std::vector<std::string> input = {"2", "3", "1", "*", "+", "9", "-"};
 
    float answer = others::postfix_expression::postfix_evaluation(input);
 
    assert(answer == -4);
}

static void test_function_2() {
    std::vector<std::string> input = {"100", "200", "+", "2", "/",
                                      "5",   "*",   "7", "+"};
    float answer = others::postfix_expression::postfix_evaluation(input);
 
    assert(answer == 757);
}
 
static void test_function_3() {
    std::vector<std::string> input = {
        "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1",
        "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1",
        "+", "+", "+", "+", "+", "+", "+", "+", "+", "+", "+",
        "+", "+", "+", "+", "+", "+", "+", "+", "+", "+"};
    float answer = others::postfix_expression::postfix_evaluation(input);
 
    assert(answer == 22);
}
 
static void test_single_input() {
    std::vector<std::string> input = {"1"};
    float answer = others::postfix_expression::postfix_evaluation(input);
 
    assert(answer == 1);
}
 
static void test_not_enough_operands() {
    std::vector<std::string> input = {"+"};
    bool throws = false;
    try {
        others::postfix_expression::postfix_evaluation(input);
    } catch (std::invalid_argument &) {
        throws = true;
    }
    assert(throws);
}
 
static void test_not_enough_operands_empty_input() {
    std::vector<std::string> input = {};
    bool throws = false;
    try {
        others::postfix_expression::postfix_evaluation(input);
    } catch (std::invalid_argument &) {
        throws = true;
    }
    assert(throws);
}
 
static void test_too_many_operands() {
    std::vector<std::string> input = {"1", "2"};
    bool throws = false;
    try {
        others::postfix_expression::postfix_evaluation(input);
    } catch (std::invalid_argument &) {
        throws = true;
    }
    assert(throws);
}

int main() {
    test_function_1();
    test_function_2();
    test_function_3();
    test_single_input();
    test_not_enough_operands();
    test_not_enough_operands_empty_input();
    test_too_many_operands();
 
    std::cout << "\nTest implementations passed!\n";
 
    return 0;
}