The Basics

Two type of values

Constants & Variables

Declaration

let keyword = "Hello, swift"

It cannot be changed or redefined once defined.

var keywork = "Hello, swift"

It is able to be changed later but not be changed the name.

Just use colon after the name to add a type annotation,

let keyword: String
var keyword2: String

Or, you can declare multiple variables in same type just on a single line, separated by commas:

let keyword = "Hello, swift", keyword2 = "Hello, Dan", keyword3 = "Hello, Kev"
var keyword, keyword2, keyword3: String

Print

Just use print(_:separator:terminator:) function to output the value in console.

let keyword = "Hello, swift"

print(keyword) //will show "Hello, swift" in console

print("The current value of keyword is \"\(keyword)\"")//will show "The current value of keyword is "Hello, swift"" in console

Numeric Literals

decimal number

we can describe it with an exponent of “e”, which means

For example:

• 1.5e2 means 1.5* = 150

Hexadecimal number

we can describe it with an exponent of “p”, which means

For example:

• 0xFp2 means 15* = 60

Tips:

We can use extra zero and underscores to make the number literal easier to read without changing its value.

For example:

let paddedDouble = 000123.456
let oneMillion = 1_000_000
let justOverOneMillion = 1_000_000.000_000_1

Tuples

If we only need one value of tuple, we can use a underscore to handle the value, just like this:

let http404Error = (404, "Not Found")
let (justTheStatusCode, _) = http404Error
print(justTheStatusCode)// will print "404"

Or you can just use a specific value to handle this:

let http404Error = (404, "Not Found")
let (justTheStatusCode, _) = http404Error.0
print(justTheStatusCode)// will print "404"

And we can name the individual elements in a tuple:

let http404Error = (statusCode: 404, description: "Not Found")
print(http404Error.statusCode)// will print "404"
print(http404Error.description)// will print "Not Found"

Error Handling

we can make a function tailed a throws keyword, in which if we meet some error conditions we can throw an error.

func canThrowAnError() throws {
    // can throw an error
}

do {
  try canThrowAnError()
} catch {
  //do things here if error occurs
}

Let's think!