title: Which declaration to use in swift
body: <p>I really don't know how to declare my variables in Swift, I have four options :</p>
  
  <pre><code>var value = 0.0 // I know this one declares value as a Double with the number 0.0
  var value: Float = 0.0 // This one declares value as a Float with the number 0.0
  var value: Float? // I really don't get the difference between this
  var value: Float! // and this, I just know that both of them are used to declare a variable without a value, am I right ?
  </code></pre>
  
  <p>I just want to declare a float without attributing a value, what is the best way ?</p>