Swift Note-IF statement

1. Basic use

Let num = 23

If num > 10 {

Print ("num is big")

}else If num < 0 {

Print ("num is Fushu")

}else{

Print ("num is mid")

}

In Swift, the conditional statement followed by if must be a booltype expression, as if (num) in OC cannot be used in swift

2.if Let's understanding

var optionalname:string? = Nil

var greeting = "Hello!"

If let name = optionalname {

Greeting = "Hello!!! \ (name) "

}

The If let ... in this sentence makes me confused for a long time

Why is the if followed by let name = Optionalname instead of optionname! = nil?

var optionalname:string? = Nil

var greeting = "Hello!"

If optionalname! = Nil {

Greeting = "Hello!!! \ (name) "

}

See an explanation on the StackOverflow, feel more reasonable. Link http://stackoverflow.com/questions/24004443/ Reason-for-assigning-optional-to-new-variable-in-conditional-statement-in-swift

His explanation is that the 1.if-let structure allows you to get a definite value (non-nil) and avoid crashing, because Swift is a very clear language, which avoids the possibility of errors due to developers not taking all the circumstances into account. 2. Examples are as follows:

var optionalname:string? {

get {

If Checktouchid () {

Print ("Get Optionalname")

Return "John Appleseed"

} else {

return Nil

}

}

}

var greeting = "Hello!"

If optionalname! = Nil {

Greeting = "Hello, \ (optionalname)"

}

In this code, because Optionalname's getter method is declared, the IF optionalname! = Nil and greeting = "Hello, \ (optionalname)" There are getter methods called Optionalname, that is, the Getter method executes 2 times, so there are some problems in the actual development, such as Getter method is obtained from the network, or getter method execution payment operation, 2 times is unreasonable.

So if you switch to the IF-LET structure, you won't have this problem.

Swift Note-IF statement