Daily Challenge #49 - Dollars and Cents

thepracticaldev profile image dev.to staff ・1 min read

Today's challenge requires you to create a function that will take a float and return the amount formatted in dollars and cents.

For example: 6.2 becomes $6.20

Want to propose a challenge idea for a future post? Email yo+challenge@dev.to with your suggestions!

This challenge comes from kolohelios on CodeWars. Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!


markdown guide

Here we go!


And the results:

f(.4); // "$0.40"
f(0); // "$0.00"
f(6.2); // "$6.20"

And how about some Intl?

f=a=>new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' }).format(a)

Which does a bit more, like adding commas:

f(.4); // "$0.40"
f(0); // "$0.00"
f(6.2); // "$6.20"
f(100000000.1234); // "$100,000,000.12"

Hello, I am surprised, you can call a function with ``. How come is it working?


ES6 added this functionality, called Tagged Template! A few examples can be found here: wesbos.com/tagged-template-literals/

Thanks a ton :) learnt new thing


Sometimes I just think about Rails method that does a very specific thing, type it out in console and it works

const formatDollars = money => `$${money.toFixed(2)}`;

love js


Mind rounding "errors":

> '$0.13'

Same happens in python:


It rounded up, though, so is that an error? It seems like expected behavior to me.


Go - with tests as usual

fun fact - this was the first time I wrote anything using Vim


package dollars

import (

// Dollars returns the string representation of a float as a dollar amount
func Dollars(amount float64) string {
    return fmt.Sprintf("$%.2f", amount)


package dollars

import (

var testCases = []struct {
    description string
    input       float64
    expected    string
        "only cents",
        "only dollars",
        "cents & dollars",
        "amounts with more than two decimal places round to the nearest cent",


func TestDollars(t *testing.T) {
    for _, test := range testCases {
        if result := Dollars(test.input); result != test.expected {
            t.Fatalf("FAILED: %s - Dollars(%f): %s, expected %s \n", test.description, test.input, result, test.expected)
        t.Logf("PASS: %s \n", test.description)


I'm not sure, but I think that "Sprintf" rounds to nearest integer.
Try with a value like 3.149 if still returns 3.14 or 3.15


Added additional test case to clarify current rounding behavior.


Yeah it rounds to the nearest cent in this case, the question becomes then do we want it to work that way, or do we say "Hey you don't have a full cent" so it always rounds down?


With miles separator too:

const formatMoney = money => [...`$${money .toFixed(2)}`]
  .flatMap((c, i) => (c != '.' && c != '$' && i > 3 && i % 3 == 0) ? [',', c]: [c])

// formatMoney(12123123123131232.000) => $12,123,123,123,131,232.00

Here is the simple solution with PHP:

function format_money(float $amount): string {
    $amounts = explode('.', (string)$amount);
    $moneyFormat = '$%d.%s';

    if (count($amounts) === 1) {
        $floating = '00';

        return sprintf($moneyFormat, $amounts[0], $floating);

    if (strlen($amounts[1]) === 1) {
      $floating = $amounts[1] . '0';

      return sprintf($moneyFormat, $amounts[0], $floating);

    return sprintf($moneyFormat, $amounts[0], substr($amounts[1], 0, 2));

My take at the challenge written in Haskell.

toFloat :: String -> Float
toFloat string = read string :: Float

decimalToInt :: Float -> Int
decimalToInt float =
    $ (*) 100
    $ toFloat
    $ take 5
    $ show
    $ float - (fromIntegral $ floor float)

decimalToDollar :: Float -> String
decimalToDollar float =
    ++ (show $ round float)
    ++ "."
    ++ (show $ decimalToInt float)

main :: IO ()
main = do
  putStrLn $ show $ decimalToDollar 6.2 -- "$6.20"
  putStrLn $ show $ decimalToDollar 6.227 -- "$6.23"

Try it online.

For some reason, I get imprecise floating point numbers when grabbing the decimal part of a floating point number in Haskell. I'm pretty new to this language so I must miss something. Feel free to improve my work here.


Rust Function:

fn format_dollar(price: f32) -> String {
    format!("${:.2}", price)
define_method(:us_curr) { |float| format('$%.2f', float.truncate(2)) }
us_curr 2.1256 # => "$2.12"

I thought about this problem from a financial standpoint and didn't like the default ruby or rails options that have been given so far because of how much lost revenue could be happening. Amazon for example has over a billion transactions a day (according to the first link on google). If we use 1.3 billion transactions and assume that the average fractional cents that they give up in a day of transactions is half a cent (.05). That would cost them 6.5 million dollars in lost revenue from giving up fractions of a cent. My solution just trims the number instead of rounding it.

I could see potential for wanting to round up from a business standpoint too, if the calculations are creating a price point for your product in a currency form then by all means you want to round up to still avoid that 6.5 million hit. In which case you would have to adjust the currency function.

This problem can really get interesting depending on your outlook.


Python :)

def to_currency(value: float) -> str:
    return "${:.2f}".format(value)

print(to_currency(6.2)) # $6.20


print('$%.2f' %(float(input('Give me money '))))


def maney(amount)
  "$" + '%.2f' % amount.to_f


defmodule Day49 do
  def float_to_money(float),
    do: "$#{:io_lib.format("~.2f", [float])}"

ruby <3

define_method(:format_dollar, &"$%.02f".:%)


fn format_dollars(amount: f64) -> String {
    format!("${:.2}", amount)

Here is the python code