title: Calculate the BMI, using mass and height, and use if else statements to print if the user is overweight, healthy or underweight, keep getting an error
body: <p>I keep getting this error Cannot convert return expression of type 'String' to return type 'Double' swift error</p>
  
  <p>I don't know what to try</p>
  
  <pre><code>import UIKit
  
  func calculateBmi (mass : Double, height: Double) -&gt; Double
  {
      let bmi = mass / (height * 2)
  
  if (bmi &gt; 25)
  {
      return ("Your bmi is \(bmi) therefore you are overweight")
  }
  else if (bmi &gt;= 18.5 &amp;&amp; bmi &lt; 25)
  {
      return ("Your bmi is \(bmi) therefore you are of normal weight")
  }
  else
  {
      return ("Your bmi is \(bmi) therefore you are underweight")
  }
  
  }
  
  print(calculateBmi(mass: 75, height: 1.55448))
  </code></pre>
  
  <p>This is the error i keep on getting Cannot convert return expression of type 'String' to return type 'Double' swift error</p>