-a
一元运算符分前置运算符和后置运算符
!b
c!
2 + 3
a ? b : c
受运算符影响的值叫操作数,在表达式 1 + 2
中,加号 +
是二元运算符,它的两个操作数是值 1
和 2
let a = 10
let (x, y) = (1, 2)
1 + 2
3 - 1
2 * 3
10 / 2
10 % 2
//字符串相加
"hello, " + "world" // 等于 "hello, world"
var a = 1
a += 2 //a = a + 2
1 == 1 // true
2 != 1 // true
2 > 1 // true
1 < 2 // true
1 >= 1 // true
2 <= 1 // false
let name = "world"
if name == "world" {
print("hello, world")
} else {
print("I'm sorry \(name), but I don't recognize you")
}
// 输出 "hello, world", 因为 `name` 就是等于 "world"
(1, "zebra") < (2, "apple") // true,因为 1 小于 2
(3, "apple") < (3, "bird") // true,因为 3 等于 3,但是 apple 小于 bird
(4, "dog") == (4, "dog") // true,因为 4 等于 4,dog 等于 dog
注意: Swift 标准库只能比较七个以内元素的元组比较函数。如果你的元组元素超过七个时,你需要自己实现比较运算符
let m = 30
let n = 20
let result = m > n ? m : n //30
let a = 10
var b : Int? //默认值为 nil
let c = b ?? a //10
for index in 1...5 {
print(index)
} //1 2 3 4 5
for index in 1..<5 {
print(index)
} //1 2 3 4
for index in array[2...] {
print(index)
} //3 4 5
for index in array[...3] {
print(index)
} //1 2 3 4
for index in array[..<3] {
print(index)
}//1 2 3
let flag = false
if !flag {
print("pass")
} //pass
let flag = false
let flag1 = true
if flag || flag1 {
print("pass")
} //pass
if flag && flag1 {
print("pass")
}