swift Swift 1.核心语法

Posted 2021-05-19

// Creating while loops in Swift
/*
while condition {
    // do something
}

do{
    // do something
} while condition



*/

// Switch STATEMENT
let windSpeed = 5;
switch windSpeed {
    
case 0:
    println("It couldn't be ");
    // in the case it's 0, do this
    
case 1:
    println("There's harldy a breeze.");
    // in the case it's 1, do this
    // (etc)
    
case 12 :
    println("Hurricane! Batten down the hatches!")
    // in the case it's 12, do this
    
// Swift - using ranges
case 0...3:
    println("it's vary calm")

case 4...6:
    println("A little windy");
    
default:
    //all other value
    break // to explicitly end this otherwise empty case
}

/* 
1. ... closed range operator
    0...100 
    36...99
    0...someVariable


2. ..< half-open range operator
    0..<100
    36..<99
    0..<someArray.count

the only difference is that the half-range operator does not include the number at the right side

*/

// THE if STATEMENT
var myVar_ifStatement = 1;
if myVar_ifStatement > 500 {
    //do somethings
}else if myVar_ifStatement < 500{
    // do somethings
}

//Creating for loops in Swift
//initializer ; condition; increment
for var i=0; i<100; i++ {
    //
}

// Creating for-in loops in Swift

/*
for each-item in some-collection {
    use each-item
}
*/

var total = 0
for index in 1...100{ //1...100 closed range operator
    total = total + index
}

println("The total is \(total)")

// Using for-in loops with Strings
var name = "Bob";
for eachChar in name{
    println(eachChar);
}

// Defining Functions
// !!! 
// in Swift, by default, an input parameter is constant, not variable
// for example

func paramsAreConstant( age: Int){
    // age = age + 1 not allowed, because the age is constant
}

func paramsAreConstant_var(var age: Int){
    // age = age + 1 now allowed, because the age is constant
}

func myFunction( name: String, age: Int){
    println("This is a simple funciton.");
}

// to call
//myFunction()


// Functions that return value
func myFunciton_return() -> String{
    return "hello";
}



// Using default parameter values
func myFunction_withDefaultValue(name : String = "John Doe"){
    println("hello, \(name)");
}

// to call
myFunction_withDefaultValue() // Okay output "hello, John Doe"
// !!! myFunction_withDefaultValue() // ERROR - this will not work 
myFunction_withDefaultValue(name : "Jane") // Okay output "hello, Jane"

// Using named parameters

func add(a:Int = 10, b: Int = 50){
    println("The result is \(a+b)");
}

// add(99) ERROR, compiler error
add(a: 99);
add(b: 200);
add(a:99, b:200);

var str = "Hello, playground";

var highScore:Int = 1000;
highScore = highScore + 100;

for i in 0..<100 {
    highScore = highScore + i;
}

var firstName:String = "Chip";
var isActive:Bool = true;

var myVariable: Int;

let daysInWeek = 7;

println("this is a print statement!");


//String Interpolation in Swift
let city = "Shanghai";
var day = "Saturday";
var temp = 75;
println("The hign for \(city) on \(day) is \(temp) degrees!");


// String Interpolation with Expression
var quantity = 17;
var unitPrice = 349;
println("The amount is \(quantity * unitPrice)");

//Expression using different TYPES
//Swift doesn't implicitely convert VALUES
var quantity_int: Int = 17; //Int
var unitPrice_double: Double = 349.54; // Double

//to convert, use Double(), Int(), String() etc
println("The amount is \(Double(quantity_int) * unitPrice_double)");