Swift数组的加法运算符用法：array1 += array2

var stringList1 = [String]()                                      //创建String类型空数组
var stringList2 = ["1", "3", "5", "7", "zoo", "9","zoo"]
var stringList3 :[String] = ["2", "4", "6","apple", "8", "10"]

stringList1 += stringList2                                        //把stringList2数组的所有元素添加到stringList1的末尾
print("stringList1: (stringList1)")                              //输出stringList1
stringList1 += stringList3                                     　 //把stringList3数组的所有元素添加到stringList1的末尾
print("stringList1: (stringList1)")                              //输出stringList1

运行结果：

stringList1: ["1", "3", "5", "7", "zoo", "9", "zoo"]
stringList1: ["1", "3", "5", "7", "zoo", "9", "zoo", "2", "4", "6", "apple", "8", "10"]

以上输出结果的元素无序排列，可使用数组的 sort() 方法或 sortInPlace() 方法排序，两者不同在于

sort()方法有返回值，返回一个新数组，而不改变原数组的值：

print("After sort: (stringList1.sort())")
print("stringList1: (stringList1)")

运行结果：

After sort: ["1", "10", "2", "3", "4", "5", "6", "7", "8", "9", "apple", "zoo", "zoo"]
stringList1: ["1", "3", "5", "7", "zoo", "9", "zoo", "2", "4", "6", "apple", "8", "10"]

sortInPlace()方法无返回值，会改变原数组的值：

stringList1.sortInPlace()
print("stringList1: (stringList1)")

运行结果：

stringList1: ["1", "10", "2", "3", "4", "5", "6", "7", "8", "9", "apple", "zoo", "zoo"]

+=运算符只能用于数组之间，不能添加单个元素：

var str = "myString"
stringList1 += str         //此行报错：Binary operator '+=' cannot be applied to operands of type '[String]' and 'String'