nil 運算子，範圍運算子，for in 迴圈

nil 運算子
正常的type = optional Int ?? 0 <----不明確宣告
let defaultColorName = "red";
var userDefinedColorName:String?;
var colorNameForUser = userDefinedColorName ?? defaultColorName;

範圍運算子
1...5   1,2,3,4,5
1..<5  1,2,3,4
for in 迴圈
for index in 1...5 {
     print(index)
}
let names = ["Anna", "Alex", "Brian", "Jack"];
let count = name.count;
for i in 0..<count {
    names[i];
}
for name in names[2...] {
    print(name);
}
for name in names[...2] {
    print(name);
}

邏輯運算子
!    ---> not
&& ---> and
||    ---> or

let allowedEntry = false;
if !allowedEntry {
    print("Access Denied");
}