Decimal to Fraction

[timstring]

I'm writing a script to scale recipes for my wife. In the process, I'm trying to teach this @#$ZGT123 computer how to do 3rd grade math.

Here's the brute force way of converting decimals to fractions. Fortunately, I only need things rounded to the nearest 1/8th. Figuring out how to convert Tbsp's into tsp's might be a little challenging

                $Scale = $CalcNum * $Factor;
                
                $Deno = (int)($Scale);
                $Rounded = round($Scale, 3);
                $Frac = $Rounded - $Deno;
                
                
                echo " Scale: " . $Scale . " Frac: " . $Frac;
                
                
                if ($Frac > 0 && $Frac<=.125) $Fraction = "1/8";            
                if ($Frac > .125 && $Frac<= 0.25) $Fraction = "1/4";
                if ($Frac > .25 && $Frac <= 0.333) $Fraction = "1/3";
                if ($Frac > .333 && $Frac <= .375) $Fraction = "3/8";
                if ($Frac > .375 && $Frac <= 0.5) $Fraction = "1/2";
                if ($Frac > .5 && Frac <= 0.625) $Fraction = "5/8";
                if ($Frac > .625 && $Frac <= 0.667) $Fraction = "2/3";
                if ($Frac > .667 && $Frac <= 0.75) $Fraction = "3/4";
                if ($Frac > .75 && $Frac <= 0.875) $Fraction = "7/8";
                
                if ($Frac > .875 && $Frac <= 1) 
                {
                    $Deno++;
                    $Frac=0;
                }
                
                if ($Deno > 0) $NewQty = $Deno . "&nbsp" . $Fraction;
                if ($Deno==0) $NewQty = $Fraction;
                if($Frac == 0) $NewQty = $Deno;
                
                echo "&nbsp;New:  &nbsp;" . $NewQty;
                
                echo "<br /><br />"; 

I'm getting one result that don't make sense. When

$CalcNum = 3.5 & $Factor = .667, $Scale = 2.333345
$Rounded = .333
$Frac = .333
$Fraction = "3/8" ??? Should be "1/3";

However, on my calculator,
$Scale = 2.3345 then $Frac = .335, yielding $Fraction as "3/8" instead of "1/3".

Why the discrepancy between the big box and the little one?


tim

"If builders built buildings the way that programmers write programs, the first woodpecker to come along would wreck civilization."

[traq]

...When $CalcNum = 3.5 & $Factor = .667, $Scale = 2.333345

...you sure about that?

protip: computers don't have 3rd-grade brains.

try it for yourself:

<?php

$Scale = 3.5 * .667;
print $Scale;

[Bonesnap]

This is why I wish everything was in metric.

Figuring out how to convert Tbsp's into tsp's might be a little challenging

Actually that's the easy part. A tablespoon is three teaspoons.

[traq]

Your current code will work "well enough" for your purposes if you just adjust your scale a bit - round to the nearest desired fraction, instead of always rounding up; i.e., instead of this:

if ($Frac > 0 && $Frac<=.1875) $Fraction = "1/8";             
if ($Frac > .125 && $Frac<= 0.25) $Fraction = "1/4"; 
if ($Frac > .25 && $Frac <= 0.333) $Fraction = "1/3";
// . . .etc. 

use something like this:

if ($Frac > 0 && $Frac<=.125) $Fraction = "1/8";             
if ($Frac > .1875 && $Frac<= 0.2915) $Fraction = "1/4"; 
if ($Frac > .2915 && $Frac <= 0.354) $Fraction = "1/3";
// . . .etc.