比较 swift 中的双值

Question

I want to compare two double values in swift

var first_value = 10.20
var second_value = 20.30
if first_value > second_value
   println("some statement")

how can we compare this type of stuff..

Answer 1

The first thing you learn in Swift is {} are mandatory for all if, if else, and else statements.

So, your code should look like this:

 var first_value = 10.20
 var second_value = 20.30

 if first_value > second_value {
     print("first_value is greater than second_value")
 }
 else {
     print("first_value is not greater than second_value ")
 }

Answer 2

You should'n use '>', '<' and '=' signs to compare float or double. Especially for comparison of close values (float i = 0.56; float j = 0.56; time to time you'll get wrong results in comparison i == j). You should use constants from float.h, as it is described here .

Answer 3

Comparing 2 double numbers using binary signs <,>, == is not entirely correct because of the device of this type of data in the computer's memory. For example, compare 2 double values:

var a: Double = 10.0
var b: Double = 10.0
print(a == b) // false

So, you need determine decimal place precision for comparison.

public extension Double {
    func greaterThan(_ value: Double, precise: Int) -> Bool {
        let denominator: Double = pow(10.0, Double(precise))
        let maxDiff: Double = 1 / denominator
        let realDiff: Double = self - value

        if fabs(realDiff) >= maxDiff, realDiff > 0 {
            return true
        } else {
            return false
        }
    }

    func greaterThanOrEqual(_ value: Double, precise: Int) -> Bool {
        let denominator: Double = pow(10.0, Double(precise))
        let maxDiff: Double = 1 / denominator
        let realDiff: Double = self - value

        if fabs(realDiff) >= maxDiff, realDiff >= 0 {
            return true
        } else if fabs(realDiff) <= maxDiff {
            return true
        } else {
            return false
        }
    }

    func lessThan(_ value: Double, precise: Int) -> Bool {
        let denominator: Double = pow(10.0, Double(precise))
        let maxDiff: Double = 1 / denominator
        let realDiff: Double = self - value

        if fabs(realDiff) >= maxDiff, realDiff < 0 {
            return true
        } else {
            return false
        }
    }

    func lessThanOrEqual(_ value: Double, precise: Int) -> Bool {
        let denominator: Double = pow(10.0, Double(precise))
        let maxDiff: Double = 1 / denominator
        let realDiff: Double = self - value

        if fabs(realDiff) >= maxDiff, realDiff <= 0 {
            return true
        } else if fabs(realDiff) <= maxDiff {
            return true
        } else {
            return false
        }
    }

    func equal(_ value: Double, precise: Int) -> Bool {
        let denominator: Double = pow(10.0, Double(precise))
        let maxDiff: Double = 1 / denominator
        let realDiff: Double = self - value

        if fabs(realDiff) <= maxDiff {
            return true
        } else {
            return false
        }
    }
}

Usage:

var a: Double = 10.0
var b: Double = 10.0
print(a.equal(a, precise: 3)) // true

Answer 4

Updated Ans

        var first_value = 10.20
        var second_value = 20.30

        if first_value.isLess(than: second_value) {
            print("first_value is not greater than second_value ")
        } else {
            print("first_value is greater than second_value ")
        }

Answer 5

Please read intro chapters to basic swift syntax:

var first_value = 10.20
var second_value = 20.30
if first_value > second_value {
    println("some statement")
}