浮动divison和铸造在Swift [英] Float divison and casting in Swift

问题描述

我试图学习Swift，我做了一个简单的平均函数：

  func average 。） - > Float {
 var sum = 0 
数字中的数字{
 sum + = number 
} 
 return Float（sum）/ Float（numbers.count）
} 
 average（1,2,3,4,5,6）
  

这给了我正确的结果：3.5
然而，我想知道为什么我必须把两个sum和numbers.count转换为浮点数。我试过这样做：

  return Float（sum / numbers.count）
  
 
 
 
但它只给我3.0 
解决方案
 ，你应该使用Double而不是Float。浮动给你非常有限的精度。为什么你想要6位数字精度与浮点，当你可以有15位数字与双是很难理解。 
 
 
 
其次，编译器完全按照你的说法。 
  Float（sum）/ Float（numbers.count）
  
取整数sum，取整数numbers.count，将两者转换为Float和divides。浮点除法得到的结果在这种情况下为3.5。 
  Float（sum / numbers.count）
  
将整数sum除以整数numbers.count。整数除法得到一个整数结果，这是整数商，不考虑任何余数。 21/6等于3，余数为3.所以除法的结果是3，然后你转换为Float 3.0。 
 
I'm trying to learn Swift and I made a simple average function:
func average(numbers: Int...) -> Float {
    var sum = 0
    for number in numbers {
        sum += number
    }
    return Float(sum)/Float(numbers.count)
}
average(1,2,3,4,5,6)
This gives me the correct result: 3.5
However, I am wondering why I have to cast both sum and numbers.count to floats. I tried casting this way:
return Float(sum/numbers.count)
but it gives me just 3.0
解决方案
First, you should use Double and not Float. Float gives you very limited precision. Why you would want 6 digits precision with Float when you could have 15 digits with Double is hard to understand. 

Second, a compiler does exactly what you tell it. 
Float (sum) / Float (numbers.count)
takes the integer "sum", takes the integer "numbers.count", converts both to Float and divides. Divison of Float gives a result in this case of 3.5. 
Float (sum/numbers.count)
divides the integer "sum" by the integer "numbers.count". Division of integers gives an integer result, which is the integer quotient disregarding any remainder. 21 / 6 equals 3 with a remainder of 3. So the result of the division is 3, which you then convert to the Float 3.0. 

                        
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