This application to implement a simple currency read service with .NET. which allow client application send a request with a valid decimal number and return a string representation of that number in the human reading format
Example :
Input: 123.45
Output: ONE HUNDRED AND TWENTY-FIVE DOLLAR AND FOURTY-FIVE CENTS
I come with a simple approach. each number will have 2 part before decimal and after the decimal. The number after decimal is Cents and before is Dollars amount
Example: 123.45$
Part1: 123$
part2 : 45
The reading number will become simple by reading the chunks of 3 digits then add the unit after those 3 digits.
Read(part1) + DOLLARS + Read(part2) +CENTS
To read Part1, we split full number to multiple chunks, each chunk has 3 digits and we start in reverse order of number because we want to read from small unit first. In this example I used a string function to split chunks, we can also use Linq or just a simple using divide and module to get the chunk number. The reason I want to use string because it will help to process a very big number that exceeds MaxValue of Int46 (ulong).
After we have a chunk of 3 digits, use be logic below to read 3 digits to string.
we define an array to mapping number to reading a word we need 3 arrays as below
string[] NUMBERS = new string[] { "", "ONE", "TWO", "THREE", "FOUR", "FIVE", "SIX", "SEVEN", "EIGHT", "NINE", "TEN" };
string[] TYS = new string[] { "", "TWENTY", "THIRTY", "FOURTY", "FIFTY", "SIXTY", "SEVENTY", "EIGHTY", "NINETY" };
string[] TEENS = new string[] { "", "ELEVEN", "TWELVE", "THIRTEEN", "FOURTEEN", "FIFTEEN", "SIXTEEN", "SEVENTEEN", "EIGHTEEN", "NINETEEN" };
If the number <= 10 , just return NUMBERS[number] + unit. for example Read(9, " Cents") => NUMBERS[9] +unit = NINE CENTS
If the number < 20 , just return TEENS[number] + unit. for example Read(9, " Cents") => TEENS[19] +unit = NINTEEN CENTS
IF Number >=20 and <100, function will return TYS[number/10] +"-" + NUMBER[number%10] + unit
`Example : 45 = TYS[4] +"-" + NUMBERS[5] = "FOURTY-FIVE" + UNIT (DOLLARS, CENT, ...)
And for all those number >=100 the rules is return the number of firt digit + apply the same logic for 2&3 digit.
return NUMBERS[number/100] " HUNDRED " + " AND "+ ReadNumber(number%100,"") + Unit`example :345 = NUMBERS[3] + ReadNumber(45) = THREE HUNDRED AND FOURTY-FIVE DOLLARS
When the input is zero the ReadNumber will return string empty in that case we don't concac it to the end result.
`Example: 400 = NUMBERS[4] + " HUNDRED " (We do not add AND here because 00 return empty.)
public string ReadNumber(int number, string unit="") {
if (number == 0) return string.Empty;
if (number <= 10) return NUMBERS[number] + unit;
if(number< 20) return TEENS[number-10] + unit;
int ten = number % 10;
int ty = number / 10;
if (number < 100) {
return string.Format(ten == 0?"{0}":"{0}-{1}", TYS[ty-1], NUMBERS[ten]) + unit;
}
int hundres = number / 100;
string secondPart = ReadNumber(number % 100);
return NUMBERS[hundres] + " HUNDRED" + (string.IsNullOrEmpty(secondPart)?"":" AND " + secondPart) + unit;
}Chunks is equipvalent to group of
string[] GROUPS = new string[] {" DOLLARS", " THOUSAND", " MILLION", " BILLION", " TRILLION"};After split the chunk to 3 digit, we will call ReadNumber(chunk, group). we do this in a loop until finish all the chunks and concac the number together. There also few logic check to ignore empty chunk such as "000" .
int pos = fullNumberStr.Length;
int chunks = 0;
string results = "";
int chunkValue = 0;
while(pos > 0) {
if(chunkValue>0) {
results = " AND " + results;
}
string chunk = fullNumberStr.Substring(Math.Max(pos - 3, 0), Math.Min(pos, 3));
chunkValue = int.Parse(chunk);
string readChunk = ReadNumber(chunkValue, GROUPS[chunks]);
pos -= 3;
if (chunkValue ==0 && pos>0 && chunks ==0) {
readChunk = GROUPS[chunks];
}
chunks++;
results = readChunk + results;
}The final end string will be this full number concat with cents amount
if (string.IsNullOrEmpty(results)) return readCents;
return results + (string.IsNullOrEmpty(readCents)?"" : (" AND " + readCents));The application shipped with a xUnit test which covert many cases to test number from 1 cents to 999 Trillion dollars
The test project can be run from visual studio or by dotnet test command
dotnet test akqa-codechallenge/akqa-codechallenge.test.csproj
This application using .NET Core 2.0, If you are a developer with Visual Studio 2017 installed, just need to open and run it as a normal project.
If you don't have visual studio, Please download .NET Core SDK to build and run it
after clone source to your local machine, please run below command
cd akqa-codechallenge
dotnet restore
dotnet run
The backend is MVC Web API which can be used by any client application using Http POST request
EndPoint :$HOST/api/v1/converter
{
"InputNumber": 123.123
}Content-Type: Application/json
Service will return below error code
This error return when you send invalid format, invalid number, or using the wrong decimal symbol.
This error return when content type is not set to application/json
Then using the wrong method, This API only support HTTP Post
Return when the server failed to read your valid input number. this will happen when the input >=1000 Trillion. API V2 will add support for bigger number later.
This is return when server accepts the request and successful to process data. The response body is json format of object look like
{"number":123456789.0,"read":"ONE HUNDRED AND TWENTY-THREE MILLION AND FOUR HUNDRED AND FIFTY-SIX THOUSAND AND SEVEN HUNDRED AND EIGHTY-NINE DOLLARS","success":true}read: the human read string of your input
number: your original number rounded to 2 decimal place
There is an issue with a singular, for example, it always read Cents and Dollars for just 1 cent or 1 dollar. This is not hard to fix. I may fix it later
If you encounter any issue, contact me samuraitruong@hotmail.com