Temperature conversion

Temperature conversion is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

There are quite a number of temperature scales. For this task we will concentrate on 4 of the perhaps best-known ones: Kelvin, Celcius, Fahrenheit and Rankine.

The Celcius and Kelvin scales have the same magnitude, but different null points.

0 degrees Celcius corresponds to 273.15 kelvin.

0 kelvin is absolute zero.

The Fahrenheit and Rankine scales also have the same magnitude, but different null points.

0 degrees Fahrenheit corresponds to 459.67 degrees Rankine.

0 degrees Rankine is absolute zero.

The Celcius/Kelvin and Fahrenheit/Rankine scales have a ratio of 5 : 9.

Write code that accepts a value of kelvin, converts it to values on the three other scales and prints the result. For instance:

K  21.00

C  -252.15

F  -421.87

R  37.80

D

<lang d>import std.stdio, std.conv, std.string;

void main(string[] args) {

   if (args.length == 2 && isNumeric(args[1])) {
       immutable kelvin = to!double(args[1]);
       if (kelvin >= 0) {
           writefln("K  %2.2f", kelvin);
           writefln("C  %2.2f", kelvinToCelsius(kelvin));
           writefln("F  %2.2f", kelvinToFahrenheit(kelvin));
           writefln("R  %2.2f", kelvinToRankine(kelvin));
       } else writefln("%2.2f K is below absolute zero", kelvin);
   }

}

double kelvinToCelsius(in double k) pure nothrow {

   return k - 273.15;

}

double kelvinToFahrenheit(in double k) pure nothrow {

   return k * 1.8 - 459.67;

}

double kelvinToRankine(in double k) pure nothrow {

   return k * 1.8;

}

unittest {

   import std.math;
   assert(approxEqual(kelvinToCelsius(21.0), -252.15));
   assert(approxEqual(kelvinToFahrenheit(21.0), -421.87));
   assert(approxEqual(kelvinToRankine(21.0), 37.8));

}</lang>

Output:

K  21.00

C  -252.15

F  -421.87

R  37.80