class Student {
    var name = "马超"
    func study(){
        
    }
}
let stud = Student()
stud.study()


class Middle_School_Student: Student {
    var Grade :Double = 100.0
    override func study() {
        
        super.study()
    }
}
let obj1 = Middle_School_Student()
obj1.Grade=99.0
obj1.study()


class University_Student: Student {
    var profession = "计算机"
    override func study() {
        super.study()
    }
    
}
let obj2 = University_Student()
obj2.profession="高翻"
obj2.study()
//字符串
var str1:String = "maChao"
var str2:String=""
str1.append("21")
str2.append(str1)

print(str2)
print(str2.count)

if str1 == str2{
    print("相等")
}else{
    print("不相等")
}

//首字母大写
var str3:String=""
str3.append(str1.capitalized)
print(str3)

 str2 = str1.replacingOccurrences(of: "21", with: "100")
print(str2)

let str4 = "八位校训"

let str5 = String(str4.reversed());
print("\n" + str5)