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var a = 1
a += 2
// a is now equal to 3
表达式 a += 2 比 a = a + 2更精炼。加法赋值运算符能够有效地把加法和赋值组合到一个运算,同时执行这两个任务。
1 == 1 // true, because 1 is equal to 1
2 != 1 // true, because 2 is not equal to 1
2 > 1 // true, because 2 is greater than 1
1 < 2 // true, because 1 is less than 2
1 >= 1 // true, because 1 is greater than or equal to 1
2 <= 1 // false, because 2 is not less than or equal to 1
let name = "world"
if name == "world" {
println("hello, world")
} else {
println("I'm sorry (name), but I don't recognize you")
}
// prints "hello, world", because name is indeed equal to "world"
var a = 1
a += 2
// a is now equal to 3
表达式 a += 2 比 a = a + 2更精炼。加法赋值运算符能够有效地把加法和赋值组合到一个运算,同时执行这两个任务。
要注意的是，复合赋值操作符不返回值。例如，你不能写让成let b = + = 2,这种行为不同于上面提到的递增和递减运算符。
复合赋值运算符的完整列表可以在[Expressions]那一章节找到
比较运算符
Swift支持所有标准c的比较运算符
等于 (a == b)
不等于(a != b)
大于 (a > b)
小于 (a < b)
大于等于 (a >= b)
小于等于(a <= b)
注：Swift 提供两个恒等运算符(=== and !==)，用它来测试两个对象引用是否来自于同一个对象实例。详见Classes and Structures。 每个比较操作符返回一个Bool值来表示语句是否为真：
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1 == 1 // true, because 1 is equal to 1
2 != 1 // true, because 2 is not equal to 1
2 > 1 // true, because 2 is greater than 1
1 < 2 // true, because 1 is less than 2
1 >= 1 // true, because 1 is greater than or equal to 1
2 <= 1 // false, because 2 is not less than or equal to 1
比较操作符通常用在条件语句，如if语句：
复制代码let name = "world"
if name == "world" {
println("hello, world")
} else {
println("I'm sorry (name), but I don't recognize you")
}
// prints "hello, world", because name is indeed equal to "world"
