php function - Working with coin values

Question

Good evening , I’d like your help in solving a problem. Researching a little here I ended up finding a code that will help me at work with a page for spending and income registration.

I would like to ensure that this code does not round up the figures. when I type 0.3 cents it returns 1. If I type 0.030 it returns 1 too and so on. I wish I could work with the right decimal places because otherwise the final values won’t match my grades.

    function format_amount($n, $n_decimals) {
    return ((floor($n) == round($n, $n_decimals)) ? number_format($n).'.00' : number_format($n, $n_decimals));
}

Thanks in advance.

Source: https://github.com/santanumajumdar/MoneyManager/blob/master/includes/Functions.php

Answer 1

The function round() is almost identical to function number_format(). To difference is that the second adds zeros to the right of the number if the value of the second parameter is greater than the number of boxes decimals of the first parameter. If the second parameter is omitted or is equal to 0, the number shall be rounded to the next integer if the decimal is equal to or greater than .5, or to the above, if the decimal is less than .5.

Exs.:

round(0.3,2); retorna 0.3
number_format(0.3,2); retorna 0.30
round(0.35); retorna 0
number_format(0.35); retorna 0
round(0.55); retorna 1
number_format(0.51); retorna 1

First suggestion is to remove from function format_amount($n, $n_decimals) the parole within the return, which becomes unnecessary, leaving only return number_format($n, $n_decimals);, in this way:

function format_amount($n, $n_decimals) {
    return number_format($n, $n_decimals);
}

The second suggestion is never send $n_decimals as 0 or less than the number of decimal places of the number in $n. If this is not observed, there is a risk of rounding. See:

format_amount('0.3', '1') // ok! 1 casa decimal e 1. Irá retornar 0.3
format_amount('0.3', '2') // ok! 1 casa decimal e 2. Irá retornar 0.30

format_amount('0.35', '1') // errado! 2 casas decimais e 1. Irá retornar 0.4
format_amount('0.353', '2') // errado! 3 casas decimais e 2. Irá retornar 0.35
format_amount(0.353,0); // errado! 3 casas decimais e 0. Irá retornar 0 (igual a round)
format_amount(0.553,0); // errado! 3 casas decimais e 0. Irá retornar 1 (igual a round)
format_amount(0.557,2); // errado! 3 casas decimais e 2. Irá retornar 0.56 (igual a round)