A small case of book borrowing

This small case, the main practice of the creation and invocation of classes and methods

voidMain () { while(true) {Console.WriteLine ("Please enter a title or author"); varKey =Console.ReadLine ().            Trim (); Library.search (Key).        Dump (); Console.WriteLine ("Please enter the number of the book to be borrowed/returned"); varID =Convert.ToInt32 (Console.ReadLine ()); varBook =Library.search (ID);                Library.changestatus (book); Console.WriteLine ("do you want to continue? y/n"); if(Console.ReadLine (). ToLower ()! ="Y". ToLower ()) { Break; }    }}classlibrary{Private Static ReadOnlyList<book> Books =NewList<book>{        NewBook (1,"Red Mansions","Cao Xueqin", Status. has been returned),NewBook (2,"Journey to the","Wu Chengen", Status. has been returned),NewBook (3,"Outlaws","Shi Naian", Status. has been returned),NewBook (4,"Kingdoms","in Luo Guanzhong", Status. has been returned)};  Public StaticIenumerable<book> Search (stringkey) {        foreach(varBookinchBooks) {            if(Book. Title.contains (key) | |Book . Author.contains (key)) {yield returnBook ; }        }            }         Public StaticBook Search (intID) {        foreach(varBookinchBooks) {            if(Book. id==ID) {returnBook ; }        }        return NULL; }         Public Static voidchangestatus (book book) {if(book!=NULL)        {            if(Book. status==Status. Returned) {Console.WriteLine ("Book Lending success"); Book. Status=Status. has been borrowed; }Else{Console.WriteLine ("successful return of the book"); Book. Status=Status. has been returned; }        }    }}classbook{ Public intId;  Public stringTitle;  Public stringAuthor;  PublicStatus status;  PublicBook (intIdstringTitlestringauthor,status Status) {Id=ID; Title=title; Author=author; Status=status; }         Public stringInfo () {return string. Format ("Id:{0}\ttitle:{1}\tauthor:{2}\tstatus:{3}", Title,author,status); }}enumstatus{has been borrowed, has been returned}

A small case of book borrowing