Swift:
Rounding numbers

How to:

Swift provides several ways to round numbers. Here’s a taste:

let original = 3.14159

// Standard rounding
let standardRounded = round(original) // 3.0

// Rounding to specific decimal place
let decimalRounded = Double(round(original * 1000) / 1000) // 3.142

// Rounding down
let roundedDown = floor(original) // 3.0

// Rounding up
let roundedUp = ceil(original) // 4.0

print("Standard: \(standardRounded), Decimal: \(decimalRounded), Down: \(roundedDown), Up: \(roundedUp)")

Output: Standard: 3.0, Decimal: 3.142, Down: 3.0, Up: 4.0

Deep Dive

Historically, rounding is a mathematical concept predating computers, essential in commerce and science. Swift’s Foundation framework offers comprehensive rounding functionality:

• round(_: ) is good old half-up rounding.
• floor(_: ) and ceil(_: ) handle directional rounding.
• rounded(.up/.down/.toNearestOrAwayFromZero) gives finer control with rounding rules enum.

Be aware of the Decimal type for precise financial calculations, which avoids floating-point errors. Also, explore NSDecimalNumber for Objective-C compatibility.

See Also

• IEEE Standard for Floating-Point Arithmetic (IEEE 754): IEEE 754