Question

我正在xcode / swift为我的女儿写一个数学测验应用。
具体来说，我想产生一个问题，其中至少包含一个负数，要对第二个随机生成的数字加上或减去。
不能是两个正数。

即。

什么是（-45）减去12？
什么是23减（-34）？

我正在努力使语法正确生成数字，然后决定所述数字是负数还是正数。

然后第二个问题是随机化，如果问题是加法或减法。

Answer 1

这是我的尝试。尝试在游乐场中运行它，它应该有希望得到你想要的结果。我希望我已经做得够干净了......

//: Playground - noun: a place where people can play

import Cocoa


let range = Range(uncheckedBounds: (-50, 50))

func generateRandomCouple() -> (a: Int, b: Int) {
    // This function will generate a pair of random integers
    // (a, b) such that at least a or b is negative.

    var first, second: Int

    repeat {
        first   = Int(arc4random_uniform(UInt32(range.upperBound - range.lowerBound))) - range.upperBound
        second  = Int(arc4random_uniform(UInt32(range.upperBound - range.lowerBound))) - range.upperBound
    }
        while (first > 0 && second > 0);

    // Essentially this loops until at least one of the two is less than zero.

    return (first, second)
}


let couple = generateRandomCouple();
print("What is \(couple.a) + (\(couple.b))")
// at this point, either of the variables is negative


// I don't think you can do it in the playground, but here you would read
// her input and the expected answer would, naturally, be:

print(couple.a + couple.b)

无论如何，请随时要求澄清。祝你好运！

Answer 2

可以在不重复数字绘制的情况下解决此问题。我的想法是：

绘制一个正数或负数的随机数
如果数字为负数：从同一范围中抽取另一个数字并返回该对。
如果数字为正数：从约束为负数的范围中绘制第二个数字。

以下是实施：

extension CountableClosedRange where Bound : SignedInteger {

    /// A property that returns a random element from the range.
    var random: Bound {
        return Bound(arc4random_uniform(UInt32(count.toIntMax())).toIntMax()) + lowerBound
    }

    /// A pair of random elements where always one element is negative.
    var randomPair: (Bound, Bound) {
        let first = random
        if first >= 0 {
            return (first, (self.lowerBound ... -1).random)
        }
        return (first, random)
    }
}

现在你可以写......

let pair = (-10 ... 100).randomPair

...并获得一个随机元组，其中一个元素保证为负数。

为测验生成随机（正面和负面）数字

2 个答案: