Xcode“无法将'String'类型的返回表达式转换为返回类型'Float'”

I am trying to create a BMI calculator that takes the user's height and weight as inputs then calculates their BMI; from there, it uses a series of if-else statements to return a message to the user that states if they are healthy/over/underweight. I have no problem getting the program to return the calculated BMI value; but when I incorporate the if-else statement, I get the "Cannot convert return expression of type 'String' to return type 'Float'" error.

我正在尝试创建一个BMI计算器，将用户的身高和体重作为输入，然后计算他们的BMI;从那里开始，它使用一系列if-else语句向用户返回一条消息，告知用户是否健康/过度/不足。我没有问题让程序返回计算出的BMI值;但是当我合并if-else语句时，我得到“无法转换类型'String'的返回表达式以返回类型'Float'”错误。

Here's my code (I've only done one if-else statement so far):

这是我的代码（到目前为止我只做了一个if-else语句）：

import UIKit

func bodyMassIndex (userHeight : Float, userWeight : Float) -> String {

    let userHeightSquared = (userHeight*userHeight)

    let userWeight = userWeight

    let userBMI = (userWeight/userHeightSquared)

    return userBMI

    if userBMI > 25 {
      return "Overweight"
    } 
}

print(bodyMassIndex (userHeight : 1.82, userWeight: 90.7))

2 个解决方案

#1

You just have to wrap the Float value of userBMI into a String.

您只需将userBMI的Float值包装到String中即可。

func bodyMassIndex (userHeight : Float, userWeight : Float) -> String {

    let userHeightSquared = (userHeight*userHeight)

    let userWeight = userWeight

    let userBMI = (userWeight/userHeightSquared)

    return String(userBMI)

    if userBMI > 25 {

        return "Overweight"

    } 
}

#2

Your logic looks a little confused here:

你的逻辑看起来有点困惑：

return userBMI
if userBMI > 25 {
    return "Overweight"
}

What is your function supposed to do? Return a BMI number, or a descriptive String? (It's trying to do both, and the compiler isn't happy)

你的功能应该是什么？返回BMI号码或描述性字符串？（它试图做到这两点，并且编译器不满意）

If I were a user, I'd want to see both the number and a statement about what it means - so you'd need two functions:

如果我是一个用户，我想看到数字和声明它的意思 - 所以你需要两个功能：

func bodyMassIndex (userHeight : Float, userWeight : Float) -> String {
  let userHeightSquared = (userHeight*userHeight)
  let userWeight = userWeight
  let userBMI = (userWeight/userHeightSquared)
  return userBMI
}

func bodyMassDiagnosis (bodyMassIndex : Float) {
  if userBMI > 25 {
    return "Overweight"
  }
  return "You're doing fine"
}

And then:

接着：

let bodyMassIndex = bodyMassIndex(height, weight)
let diagnosis = bodyMassDiagnosis(bodyMassIndex)
self.indexLabel.text = "BMI \(bodyMassIndex)"
self.diagnosisLabel.text = diagnosis

#1