Kathy Kam : Quiz

Quiz of the Month: IsDaylightSavingTime() or not?

KathyKam — Sat, 29 Jul 2006 03:04:00 GMT

Question: Given your machine is in Pacific Time (PST) Time Zone, what is MainProgram.GetAnswer so that MainProgram.Test returns true?

class MainProgram

{

static DateTime GetAnswer()

{

????

}

static bool Test()

{

DateTime a = MainProgram.GetAnswer();

String actual = String.Format("DateTime: {0}; IsDaylightSavingTime: {1}", a, a.IsDaylightSavingTime());

String expected = "DateTime: 10/29/2006 1:30:00 AM; IsDaylightSavingTime: True";

return (actual == expected);

}

static void Main(string[] args)

{

}

P.S. The answer will post in a week! I promised this time!

Note: Updated a clause here, that your machine needs to be in Pacific Time Zone

Quiz of the Month: Double Trouble

KathyKam — Tue, 09 May 2006 04:02:00 GMT

Without compiling and running this program. Can you tell me what the output would be?

class MainProgram

{

static void Main(string[] args)

{

double a = Convert.ToDouble("1.170404");

double b = Convert.ToDouble("2.170404");

double c = Convert.ToDouble("3.170404");

double d = Convert.ToDouble("4.170404");

Console.WriteLine((a == 1.170404));

Console.WriteLine((b == 2.170404));

Console.WriteLine((c == 3.170404));

Console.WriteLine((d == 4.170404));

}

Answer of the month: Type.FullName

KathyKam — Thu, 27 Apr 2006 04:22:00 GMT

Answer: It will assert.

Why: Well, first of all... there is one big reason why the assert would fire. "t1" refers to something that has to do with the DerviedClass, and "t2" refers to something that has to do with the BaseClass.

Good job Barry for noticing it. I agree with Barry, my quiz was not planned very well. (I promise to author a better quiz for May.) What I want to highlight in this example is the fact that Type.FullName returns null when the type contains generic parameters.

As Barry has mentioned, a better example is:

Type t1 = typeof(DerivedClass<>).BaseType;
Type t2 = typeof(BaseClass<>);

Anyways, with my example, what you get is this:

fullName1 = "DerivedClass`1"
fullName2 = null

Why is the FullName of t1.BaseType null?

The BaseType of DerivedClass<T> does not equal BaseClass<T>. If we use a differnt name for the generic variable in DerivedClass, you'll see why. Suppose you use S:

Foo<S>

Then the BaseType of DerivedClass is BaseClass<S>. Any type which is not a generic type definition and containsGenericArguements = true will not have a FullName because we do not provide a syntax for resolving generic paramenters. Why didn't we provide a syntax you may ask... This is because the general problem is made difficult in the case where the generic parameter belongs to a method. In order to identify the generic paramenter, we'll have to provide overload resolution. In this example, what would you expect the Fullname to be for the instatiation Foo<S> given the defintion:

class Foo<T>
class Class
void Bar<S>()
void Bar<R>(int i)

Also, Haibo also talked about it here.

Quiz of the month: Type.FullName

KathyKam — Sat, 08 Apr 2006 04:38:00 GMT

I once had a dev manager who loves puzzles and quizes. During our team meetings, he will write some code on the board and the team would have a competition to see who can spot the mistake first or who can answer a question about the code first. I always enjoyed those quiz. So I think I am going to start this on my blog. Once a month, I'll find something interesting and see who can give me the answer and an explaination why. :) Of course you can just run the code and have the right answers, but understanding why is the interesting part.

Here is my first "Quiz of the month"! I'll post the answer to this in 2 weeks.

Without running it, can you tell me whether the code below will assert? If yes, why? If not, why not?

class Prog

{

static void Main(string[] args)

{

Type t1 = typeof(DerivedClass<>);

Type t2 = t1.BaseType;

string fullName1 = t1.FullName;

string fullName2 = t2.FullName;

Debug.Assert(fullName1 == fullName2);

}

public class BaseClass<T>

{

}

public class DerivedClass<T> : BaseClass<T>

{

}