For those who have free time on their hands, and who would like to work through some brain twisters, here is a list of C# code snippets for your perusal. See https://www.toptal.com/c-sharp/top-10-mistakes-that-c-sharp-programmers-make for more details.
1.
//=============================================================================
private static void CSharpPuzzle1()
{
Point point1 = new Point(20, 30);
Point point2 = point1;
point2.X = 50;
Console.WriteLine(point1.X); // What is the output?
Console.WriteLine(point2.X); // What is the output?
Pen pen1 = new Pen(Color.Black);
Pen pen2 = pen1;
pen2.Color = Color.Blue;
Console.WriteLine(pen1.Color); // What is the output?
Console.WriteLine(pen2.Color); // What is the output?
Console.WriteLine();
}
2.
//=============================================================================
static Pen pen1;
static Point point1;
public static void CSharpPuzzle2()
{
Console.WriteLine(pen1 == null); // What is the output?
Console.WriteLine(point1 == null); // What is the output?
Console.WriteLine(point1 == default(Point));
// Note: you can't declare an auto of a value type without an initializer!
//Point p;
//p.X = 1;
Console.WriteLine();
}
3.
//=============================================================================
static void CSharpPuzzle3()
{
string s = "strasse";
// What is the output?
Console.WriteLine(s == "straße");
Console.WriteLine(s.Equals("straße"));
Console.WriteLine(s.Equals("straße", StringComparison.Ordinal));
Console.WriteLine(s.Equals("Straße", StringComparison.CurrentCulture));
Console.WriteLine(s.Equals("straße", StringComparison.OrdinalIgnoreCase));
Console.WriteLine(s.Equals("straße", StringComparison.CurrentCulture));
Console.WriteLine(s.Equals("Straße", StringComparison.CurrentCultureIgnoreCase));
Console.WriteLine(s == "strasse");
Console.WriteLine(s.Equals("strasse"));
Console.WriteLine();
}
4.
//=============================================================================
class Account
{
[Key]
public string ID { get; set; }
public string Status { get; set; }
public decimal Balance { get; set; }
}
static void CSharpPuzzle4()
{
List<Account> myAccounts = new List<Account>()
{
new Account() { Status = "active", Balance = 1 },
new Account() { Status = "inactive", Balance = 2 },
new Account() { Status = "active", Balance = 3 }
};
// What is the output?
{
decimal total = 0;
foreach (Account account in myAccounts)
{
if (account.Status == "active")
{
total += account.Balance;
}
}
Console.WriteLine(total);
}
// What is the output?
{
decimal total = myAccounts.Sum((account) => (account.Status == "active") ? account.Balance : 0);
Console.WriteLine(total);
}
}
5.
//=============================================================================
class Accounts : DbContext
{
public Accounts() : base("Accounts.DbConnection") {}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
Database.SetInitializer<Accounts>(new SocialClubInitializer());
base.OnModelCreating(modelBuilder);
}
public DbSet<Account> _accounts { get; set; }
}
class SocialClubInitializer : DropCreateDatabaseAlways<Accounts>
{
protected override void Seed(Accounts context)
{
context._accounts.Add(new Account() { ID = "1", Status = "Active", Balance = 1 }); // Note capital "A"
context._accounts.Add(new Account() { ID = "2", Status = "Inactive", Balance = 2 });
context._accounts.Add(new Account() { ID = "3", Status = "Active", Balance = 3 }); // Note capital "A"
}
}
static void CSharpPuzzle5()
{
Accounts dbc = new Accounts();
dbc.SaveChanges();
var count = dbc._accounts.Count();
{
decimal total = dbc._accounts.Sum(
(account) => (account.Status == "active") ?
(decimal?) account.Balance :
0) ?? 0;
Console.WriteLine(total); // What is the output?
}
}
6.
//=============================================================================
static void CSharpPuzzle6()
{
int[] a = new int[] {1, 3, 5, 7, 9};
int sum = a.Sum(); // Where is Sum defined?
int len = a.Length; // Where is Length defined?
}
7.
//=============================================================================
static void CSharpPuzzle7()
{
// Which implementation is faster?
// Which implementation uses more memory?
{ // Implementation A.
var before = DateTime.Now;
int size = 100000000;
bool[] a = new bool[size];
for (int i = 1; i < size; ++i) a[i] = a[i - 1];
var after = DateTime.Now;
Console.WriteLine(a.SizeOf());
Console.WriteLine(after - before);
}
{ // Implementation B.
var before = DateTime.Now;
int size = 100000000;
BitArray a = new BitArray(size);
for (int i = 1; i < size; ++i) a[i] = a[i - 1];
var after = DateTime.Now;
Console.WriteLine(a.SizeOf());
Console.WriteLine(after - before);
}
}
8.
//=============================================================================
class SystemResource : IDisposable
{
public void Dispose()
{
// The implementation of this method not described here.
// ... For now, just report the call.
Console.WriteLine(0);
}
}
static void CSharpPuzzle8()
{
// What is the output?
using (SystemResource resource = new SystemResource())
{
Console.WriteLine(1);
}
Console.WriteLine(2);
{
SystemResource leak = new SystemResource();
Console.WriteLine(3);
}
Console.WriteLine(4);
}
9.
//=============================================================================
class B { }
class D1 : B { }
class D2 : B { }
static void CSharpPuzzle9()
{
try
{
B o = new D1();
D2 c = (D2) o;
}
catch (Exception) { Console.WriteLine("Exception1"); }
try
{
B o = new D1();
D2 d = o as D2;
}
catch (Exception) { Console.WriteLine("Exception2"); }
}
10.
//=============================================================================
class CSharpPuzzle10
{
// What does the compiler output for warnings and errors?
int myId;
int Id;
CSharpPuzzle10(int id)
{
this.myId = Id;
}
}