//字符串的创建有两种
//不可变字符串
let str = "I'm a string"

//可变字符串
var string = "I'm a mutableString1"

//可变字符串初始化再赋值
var mutableString : String
mutableString = "I'm a initMutableString"

print("str = \(str)")
print("string = \(string)")
print("mutableString = \(mutableString)")

str = I'm a string
string = I'm a mutableString1
mutableString = I'm a initMutableString

let string = ""
let string1 = String()
print("voidString = \(string)")
print("voidString1 = \(string1)")

voidString = 
voidString1 = 

let string = ""
if string == ""{
    print("string 是空字符")
}else{
    print("string 不是是空字符")
}
//第二种
if string.isEmpty {
    print("string 是空字符")
}else{
    print("string 不是是空字符")
}

string 是空字符
string 是空字符

//字符串的拼接
//直接 +
var string = "abc"
 string += "def"
print("string = \(string)")
//第二种拼接\()
let str = "hij"
let str1 = "\(str)klm"  //字符串的拼接   用    \(要拼接的内容)
print("str1 = \(str1)"

string = abcdef
str1 = hijklm

let number = 3
let number1 = 2.1
let sum = "\(number) 加上 \(number1) 等于 \(Double(number) + number1)"
print("sum = \(sum)")

sum = 3 加上 2.1 等于 5.1

//字符串的长度
let string = "China,America"
let length = string.characters.count
print("length = \(length)")

length = 13

let str = "abcdefghij"
let str2 = "nmgghjkjhghj"
if str == str2 {
    print("str 和 str2 是相等的")
}else{
    print("str 和 str2 是不相等的")
}

str 和 str2 是不相等的