Swift 有三种条件判断：

• if else
• switch
• ternary 三元运算

if else

if 语句 后可以有可选的 else 语句, else 语句在布尔表达式为 false 时执行。

let level = 9001
if level > 9000 {
  print("It's over 9000! You can proceed with your quest.")
} else {
  print("Bummer, you definitely need to go for a training arc")
}

switch

switch 语句允许测试一个变量等于多个值时的情况。

let level = 10000

switch level {
   case 7000 :
     print("Muda Muda Muda Muda Muda Muda")
   case 8000 :
     print("You are not strong enough")
   case 9000 :
     print("You are strong enough! You can proceed with your quest")
   case 10000:
     print("It's over 9000! You can proceed with your quest.")
   default :
     print("Please try again")
}

ternary

switch 语句允许测试一个变量等于多个值时的情况。 Swift 语言中  只要匹配到 case 语句，则整个 switch 语句执行完成。

let level = 9000
print( level > 9000 ? "It's over 9000! You can proceed with your quest." :  print("Bummer, you definitely need to go for a training arc")