Applied Programming/Conditions/PHP

conditions.php

<?php

// This program converts a Fahrenheit temperature to Celsius.
//
// Input:
//     Fahrenheit temperature
//
// Output:
//     Fahrenheit temperature
//     Celsius temperature
//
// Example:
//     Enter Fahrenheit temperature:
//     100
//     100.0° Fahrenheit is 37.8° Celsius
//    
// References:
//     * http://www.mathsisfun.com/temperature-conversion.html
//     * http://php.net/manual/en/features.commandline.io-streams.php
//     * https://stackoverflow.com/questions/481466/php-string-to-float


define('ABSOLUTE_ZERO', -459.67);

function get_fahrenheit() {
    /* Gets Fahrenheit temperature.

    Args:
        None

    Returns:
        float: Fahrenheit temperature

    Exits:
        ValueError: If Fahrenheit temperature is not a valid float.
        ValueError: If Fahrenheit temperature is below absolute zero.

    */
    try {
        echo "Enter Fahrenheit temperature:";
        $fahrenheit = rtrim(fgets(STDIN));

        if ($fahrenheit < ABSOLUTE_ZERO) {
            throw new Exception("Fahrenheit temperature cannot be below 
                absolute zero.");
        
        } elseif (!(is_numeric($fahrenheit))) {
            throw new Exception("Fahrenheit temperature must be a floating 
                point value.");
        }        
        return $fahrenheit;

    } catch (Exception $e) {
        echo $e->getMessage() . "\n";
        echo "Value error: '" . $fahrenheit . "' is invalid.";
        exit();
    }
}

function fahrenheit_to_celsius($fahrenheit) {
    /* Converts Fahrenheit temperature to Celsius.

    Args:
        fahrenheit (float): Fahrenheit temperature to be converted

    Returns:
        float: Celsius temperature

    Exits:
        ValueError: If Fahrenheit temperature is not a valid float.
        ValueError: If Fahrenheit temperature is below absolute zero.

    */

    try {
        if (!(is_numeric($fahrenheit))) {        
            throw new Exception ("Fahrenheit temperature must be a 
                floating point value.");
        }
        elseif ($fahrenheit < ABSOLUTE_ZERO) {
            throw new Exception("Fahrenheit temperature cannot be below 
                absolute zero.");
        }
    } catch (Exception $e) {
        echo $e->getMessage() . "\n";
        echo "Received '" . $fahrenheit . "'";
        exit();
    }

    define ('TEMPERATURE_DIFFERENCE', 32);
    define ('TEMPERATURE_RATIO', 5 / 9);

    $celsius = round(($fahrenheit - TEMPERATURE_DIFFERENCE) * 
        TEMPERATURE_RATIO, 1);

    return $celsius;
}

function display_results($fahrenheit, $celsius) {
    /* Displays Fahrenheit and Celsius temperatures.

    Args:
        fahrenheit (float): Fahrenheit temperature
        celsuis (float): Celsius temperature

    Returns:
        None

    Raises:
        AssertionError: If Fahrenheit temperature is not a valid float.
        AssertionError: If Celsius temperature is not a valid float.

    */
    assert (is_numeric($fahrenheit), "Fahrenheit must be a float. 
        Received " . gettype($fahrenheit));
    
    assert (is_numeric($celsius), "Celsius must be a float. 
        Received " . gettype($celsius));

    echo $fahrenheit . "° Fahrenheit is " . $celsius . "° Celsius";
}

function main() {
    $fahrenheit = get_fahrenheit();
    $celsius = fahrenheit_to_celsius($fahrenheit);
    display_results($fahrenheit, $celsius);
}

main();

?>
Try It

Copy and paste the code above into one of the following free online development environments or use your own PHP compiler / interpreter / IDE.
conditions.php

Try It

See Also
