Split fractional and integral parts of a Double

Question

I am converting volume measures between cups and mL. The user can put in a fraction for the amount of cups, for example 3 and 1/2 cups, which would be stored as 2 variables: an Int for the whole part and a Float for the fraction. When converting to mL I can easily just make them both Doubles, add them, then multiply that by the conversion rate and make the final output an Int for a close enough approximation.

The problem is converting that back to cups. I have an integer now so I can just make it a Double and then divide it by the conversion rate (240) and get a Double that has a fraction, the main issue is, I need that to be stored as 2 variables again, an Int for the whole number (cups) and a Float for the remainder.

I can't seem to find a way to get that remainder.

float newAmount = amount/240;
int cups = Math.floor(newAmount)
float fraction = newAmount % 1

How can I get that remainder (fraction) in Swift when dividing the 2 numbers? Most of the questions on this are just how to convert a Double to an Int, which I know how to do.

I tried running a test with the truncatingRemainder and it is completely dropping the remainder. Here is the test I ran...

let constA = 6
print(constA)

let constB:Float = 0.25
print(constB)

let currentAmount = Double(constA) + Double(constB)
print(currentAmount)

let newAmount = currentAmount * 240
print(newAmount)
let finalInt = Int(newAmount)
print(finalInt)

let conversionAmount = Double(finalInt) / 240
print("conversion: \(conversionAmount)")
let remainder = newAmount.truncatingRemainder(dividingBy: 1)
print("remainder \(remainder)")
var fraction = 0.0
if remainder > 0.0 {
    if remainder <= 0.25 {
        fraction = 0.25
    } else if remainder <= 0.50 {
        fraction = 0.50
    } else {
        fraction = 0.75
    }
}
print(fraction)

The output of that is...

6
0.25
6.25
1500.0 
1500 
conversion: 6.25 
remainder 0.0
0.0

For some reason the truncatingRemainder(dividingBy: 1) method is dropping the .25 out of the number completely.

I would suggest storing all of these as Double and only change to rounded Int for display purposes. I would also make cups a single variable and worry about fractional rousing just before display. — Chris, Mar 05 '19 at 19:27
Why are you switching between `Float` and `Double` like that? — jscs, Mar 05 '19 at 19:34
@JoshCaswell I was converting the numbers from Float to Double because the way I understood it Double was good for really high accuracy something like 12 decimal places, but I will only ever need 1/4, 1/2, and 3/4, or .25, .50, and .75, so I thought storing them as a double in CoreData would be an overkill. I am really new to the swift language though, so if that is incorrect I would be happy to change it — Neglected Sanity, Mar 05 '19 at 19:42

Split fractional and integral parts of a Double

0 Answers0