Question

How to calculate the percentage change between two values in Swift

Answer 1

import Foundation

func percentageChange(oldValue: Double, newValue: Double) throws -> Double {
    guard oldValue != 0 else {
        throw NSError(domain: "PercentageError", code: 1,
                      userInfo: [NSLocalizedDescriptionKey: "oldValue cannot be zero"])
    }
    return ((newValue - oldValue) / oldValue) * 100.0
}

let oldValue = 45.0
let newValue = 57.0

do {
    let change = try percentageChange(oldValue: oldValue, newValue: newValue)
    print(String(format: "Percentage change: %.2f%%", change))
} catch {
    print("Error:", error.localizedDescription)
}



/*
run:

Percentage change: 26.67%

*/

 

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