visual studios express 2013 errors

我制作新程序时都会在编译时出现此错误，以前我使用 2012 并且从未遇到过这个问题，但现在我每次都看到这个：

错误：

Error   2   error LNK2019: unresolved external symbol 
"public: __cdecl lonework::App::App(void)" (??0App@lonework@@Q$AAA@XZ)
referenced in function "public: void __thiscall <lambda_b6bf150325cab1ba448790bcac21fea0>::operator()(class Windows::UI::Xaml::ApplicationInitializationCallbackParams ^)
const " (??R<lambda_b6bf150325cab1ba448790bcac21fea0>@@QBEXP$AAVApplicationInitializationCallbackParams@Xaml@UI@Windows@@@Z)    C:UsersLoganDocumentsVisual Studio 
    2013Projectsloneworkloneworklonework.WindowsXamlTypeInfo.g.obj lonework.Windows

当前处理的代码：

#include <pch.h>
#include <conio.h>
#include <stdio.h>
#include <Windows.h>
int yes();
int no();
int main()
{
    char choice;
    printf("Think of a number between one and tenn");
    Sleep(2000);
    printf("Got it yet?n Y/N ");
    scanf_s("%c", &choice,1);
    if (choice == 'y' || choice == 'Y')
    {
        printf("That's good");
        yes();
    }
    else if (choice == 'n' || choice == 'N')
    {
        printf("Are you really that slow");
        no();
    }
    getchar();
    return 0;
}
int yes()
{
    printf("Good for you, keep thinking about it...n");
    printf("Now think of another one, a different onen Got it?n I'll assume yes, sounds good.n     Now I'll tell you your number.n");
    printf("...n");
    Sleep(2000);
    printf("...n");
    Sleep(2000);
    printf("Ahem, 3 and 7");
    return 0;
}
int no()
{
    printf("Alright, back to the top.n");
    main();
    return 0;
}