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Posted on Aug 26, 2019

Daily Challenge #49 - Dollars and Cents

#challenge

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!

Top comments (24)

La blatte • Aug 26 '19 • Edited

Here we go!

f=a=>`$${a.toFixed`2`}`;

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"

Tushar Khanna • Aug 30 '19 • Edited

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

La blatte • Aug 30 '19

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

Tushar Khanna • Aug 30 '19

Thanks a ton :) learnt new thing

Mikhail Korolev • Aug 26 '19 • Edited

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

number_to_currency(number)

Jarod Smith • Aug 26 '19

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

`
love js

Sascha • Aug 26 '19 • Edited

Mind rounding "errors":

formatDollars(.126)
> '$0.13'

Same happens in python:

print(f"{123.126:.2f}")
123.13

Josh • Aug 26 '19

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

Donald Feury • Aug 26 '19 • Edited

Go - with tests as usual

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

dollars.go

package dollars

import (
    "fmt"
)

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

dollars_test.go

package dollars

import (
    "testing"
)

var testCases = []struct {
    description string
    input       float64
    expected    string
}{
    {
        "only cents",
        .04,
        "$0.04",
    },
    {
        "only dollars",
        3,
        "$3.00",
    },
    {
        "cents & dollars",
        3.14,
        "$3.14",
    },
    {
        "amounts with more than two decimal places round to the nearest cent",
        4.478,
        "$4.48",
    },

}

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)
    }
}

Tiash • Aug 26 '19

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

Donald Feury • Aug 26 '19

Added additional test case to clarify current rounding behavior.

Donald Feury • Aug 26 '19 • Edited

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?

Alfredo Salzillo • Aug 26 '19

With miles separator too:

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

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

peter279k • Jun 20 '20

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));
}

Amin • Aug 26 '19

My take at the challenge written in Haskell.

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

decimalToInt :: Float -> Int
decimalToInt float =
  round
    $ (*) 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.

Jay • Aug 27 '19

Rust Function:

fn format_dollar(price: f32) -> String {
    format!("${:.2}", price)
}

David J. Davis • Aug 29 '19 • Edited

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.

Rafael Acioly • Aug 27 '19

Python :)

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

print(to_currency(6.2)) # $6.20

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Daily Challenge #49 - Dollars and Cents

Top comments (24)

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