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Solution: The Absolute Zero Validator

Explore how to implement an Absolute Zero Validator using modern C++ features. Learn to define compile-time constants, utilize std::optional for error handling, and safely manage function results. This lesson teaches how to write clean, expressive code that handles invalid inputs gracefully without exceptions.

We'll cover the following...
C++ 23
#include <iostream>
#include <optional>
constexpr double ABSOLUTE_ZERO = -273.15;
std::optional<double> celsiusToFahrenheit(double celsius) {
    if (celsius < ABSOLUTE_ZERO) {
        return std::nullopt;
    }
    // Calculate and return the value directly; it implicitly converts to optional
    return (celsius * 9.0 / 5.0) + 32.0;
}
int main() {
    double inputTemp = -300.0; 
    std::optional<double> result = celsiusToFahrenheit(inputTemp);
    if (result.has_value()) {
        std::cout << "Temperature in F: " << result.value() << "\n";
    } else {
        std::cout << "Invalid temperature reading.\n";
    }
    // Test with a valid value
    std::optional<double> validResult = celsiusToFahrenheit(25.0);
    if (validResult) {
         std::cout << "Temperature in F: " << *validResult << "\n";
    }
    return 0;
}
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