接受 2 个正数并打印中间每个素数的代码有问题吗？ - Swift

Question

我正在尝试编写一个函数，它接受 2 个正整数并打印它们之间的每个素数，并且还包括这 2 个数字（如果它们是素数）。这就是我目前所拥有的，但它只会打印第一个数字是质数，其余的都不是。我在网上查过这个，但我似乎无法弄清楚这段代码有什么问题，因为许多其他网站都使用类似的逻辑。

func printPrimes(from firstNum: Int, to lastNum: Int) {
    var newFirstNum = firstNum
    if firstNum == 0 {
        newFirstNum = 2
    }


    let numbers = newFirstNum...lastNum


    // Goes through each number from 2-100 starting from 2.
    for number in numbers {

        var primeValue = false
        let startPoint = 2

        let number2 = startPoint...number

        // Takes current number and divides by every number from 2 to the given number.
        for currentIndex in number2 {
            primeValue = false
            if number % currentIndex != 0 {
                primeValue = true
            }
        }
            if primeValue == false {
                print("\(number) is not prime")

            } else {
                print("\(number) is prime")
            } 
    } 
}

这是我正在使用的函数调用类型：

printPrimes(from: 0, to: 100)

如有任何帮助，我们将不胜感激。

Answer 1

几个问题。主要是你设置的 primeValue 都是错误的。您首先将其设置为 false。然后，即使您已经确定该数字是质数，您也可以为您将要尝试的每个因素将其重置为 false。

在找到一个因数之前最好假设这个数是质数。你需要避免检查一个数字本身。

这是您的固定代码：

func printPrimes(from firstNum: Int, to lastNum: Int) {
    var newFirstNum = firstNum
    if firstNum == 0 {
        newFirstNum = 2
    }

    let numbers = newFirstNum...lastNum

    // Goes through each number from 2-100 starting from 2.
    for number in numbers {
        var primeValue = true // assume prime unless we find a factor
        let startPoint = 2

        let number2 = startPoint..<number // Don't include number

        // Takes current number and divides by every number from 2 to the given number.
        for currentIndex in number2 {
            if number % currentIndex == 0 {
                primeValue = false // we found a factor, not prime
                break // no need to check for any other factors
            }
        }

        if primeValue {
            print("\(number) is prime")
        } else {
            print("\(number) is not prime")
        }
    }
}

printPrimes(from: 0, to: 100)

接受 2 个正数并打印中间每个素数的代码有问题吗？ - Swift

Issue with code that takes in 2 positive numbers and prints every prime number in between? - Swift

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