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let label = "The width is "
let width = 94
let width = label + String(width)
1.4.字符串格式化
Swift使用(item)的形式进行字符串格式化：
复制代码let apples = 3
let oranges = 5
let appleSummary = "I have (apples) apples."
let appleSummary = "I have (apples + oranges) pieces of fruit."
1.5.数组和字典
Swift使用[]操作符声明数组（array）和字典（dictionary）：
复制代码var shoppingList = ["catfish", "water", "tulips", "blue paint"]
shoppingList[1] = "bottle of water"
var occupations = [
"Malcolm": "Captain",
"Kaylee": "Mechanic",
]
occupations["Jayne"] = "Public Relations"
一般使用初始化器（initializer）语法创建空数组和空字典：
复制代码let emptyArray = String[]()
let emptyDictionary = Dictionary<String, Float>()
如果类型信息已知，则可以使用[]声明空数组，使用[:]声明空字典。
2.控制流
2.1概览
Swift的条件语句包含if和switch，循环语句包含for-in、for、while和do-while，循环/判断条件不需要括号，但循环/判断体（body）必需括号：
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let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
if score > 50 {
teamScore += 3
} else {
teamScore += 1
}
}
2.2可空类型
结合if和let，可以方便的处理可空变量（nullable variable）。对于空值，需要在类型声明后添加?显式标明该类型可空。
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