Software Engineer

I am a Software Engineer. I have a Bachelor (Honours) of Science in Information Technology from the University of Sunderland - Class of 2003. I have been developing software since 2001 when I was offered a role at CERN as part of their Technical Student Programme.

By 2016 I had grown really tired of the software industry and by the end of 2019 Apple killed whatever excitement I had left. I am not sure what the next 10 years will bring. What I do know is that my apettite to do work that is impactful has only grown bigger and stronger. Great people make me tick more than anything.

I am also tired.

Making wordings of numbers 27 going twentyseven

public final class Wording
private final Map<Integer, String> wordings;

public Wording(Map<Integer, String> wordings)
    this.wordings = wordings;

public String of(int number){
return this.of(number, 10);

private String of(int number, int mod) 
    if(number == 0)
        return "";
    int value = number % mod;

     * if there is no value for a digit skip to the next mod.
     * e.g.  
     * missing units
     *  120 % 10 = 0
     * missing tens
     *  100 % 100 = 0 //missing tens
    if(value == 0) {
    return this.of(number, mod * 10);
    StringBuilder sb = new StringBuilder();

    String wording = this.wordings.get(value);
    sb.append( wording );
    int remaining = number - value;

    String stringOf = this.of(remaining, mod * 10);

    sb.insert(0, stringOf);
return sb.toString();

public class WordingTest 
public static final Map<Integer, String> wordings = 
    new HashMap<Integer, String>()
            this.put(7, "seven");                   
            this.put(20, "twenty");
            this.put(100, "onehundred");

private void assertOf(String name, int number) 
    Wording wording = new Wording(wordings);
    Assert.assertEquals(name, wording.of(number));

public void stringOfSeven() throws Exception 
    assertOf("seven", 7);

public void stringOfTwentySeven() throws Exception 
    assertOf("twentyseven", 27);

public void stringOfOneHundred() throws Exception 
    assertOf("onehundred", 100);

public void stringOfOneHundredTwenty() throws Exception 
    assertOf("onehundredtwenty", 120);

public void stringOfOneHundredSeven() throws Exception 
    assertOf("onehundredseven", 107);

public void stringOfOneHundredTwentySeven() throws Exception 
    assertOf("onehundredtwentyseven", 127);

Just recently came across this case needing to convert a number to its wording. For example, given the number 27 produce “twentyseven”.

One way to tackle this is to dissect the number to its digits one by one, starting by the lower ones.

(0)			2		7
(hundreds)	tens 	units

Using a lookup table on units, tens, hundreds will allow us to get the wording for a single number.

	Map<Integer, String> units = new HashMap<Integer, String>();
	units.put(7, "seven");

	Map<Integer, String> tens = new HashMap<Integer, String>();
	tens.put(20, "twenty");

The real question then becomes, what algorithm will give us the number of the right magnitude? In other words, how can we get the units, the tens and the hundreds of a number?

For that we will take advantage of the mod operator with a touch of recursion to traverse the whole number.

First a reminder on the mod. Whenever you mod a number, the value you get back is anywhere within the range of the modulo, starting from 0.

	27 % 10		= 	7 	(units)
	20 % 100 	= 	20 	(tens)
	0  % 1000 	=	0 	(hundreds)

With that in mind, starting from 10 as the modulo we get the value of the units, thus its wording.

Every time subtracting the current value from the number to be left with the next scale.

	27 - 7 = 20

and modding again with the next modulo

	mod * 10

until we get a 0 as the number, which is the stop condition.

What about numbers that are missing digits like 100 which will give a 0 as soon as we mod them? Well, there are a couple of ways to go about it.

  • Add a lookup value of an empty string to 0. This although works, breaks the semantics of the lookup.
  • Check for a null and use an empty string instead. In this case you will have the overhead of allocating the StringBuilder and that of the append.
  • Skip to the next mod.

There is however a serious limitation to the above. How do you go on about numbers between 11 (“eleven” and not “tenone”) through 19? What about the number 0?

Developers challenge: Implement the above in your preferred language while also coming up with an answer to the above limitation. The first one to write a solution and a test that proves it, gets a postcard from Edinburgh.

How would you improve the algorithm to produce better wordings? Do you have another algorithm to share for figuring out the wording of a number?

As always, you can find the source code of the post over at github.

Kudos to @nelstrom, the person behind Drew recently visitted Egypt and was pleased to find out that numbers are read left to right as opposed to arabic script and figuring out their wording.