Chapter 4: Using Types

Question 0

What happens during a narrowing conversion that fails for floats? (Double to float)

Answer 0

The result float is set to infinity. Check for this with float.IsInfinity (static method)

Question 1

What type does the “checked” block work for and what does it do?

Answer 1

Only for integer. It throws an exception when a narrowing conversion fails.

Question 2

Are implicit conversions allowed for narrowing conversions?

Answer 2

No

Question 3

If x were an Int32, what would you get by calling:

BitConverter.GetBytes(x)

Answer 3

An array of bytes, 4 actually.

Question 4

How is a cast handled from float to int?

Answer 4

Truncate

Question 5

System.convert.toInt32 does what to a float-to-int conversion?

Answer 5

Rounds to nearest int.

Question 6

Once you cast a reference type to an ancestor class, can you use it again later as the original type?

Answer 6

Yes. It never really changes, it’s a reference (address) after all. You can simply “convert” it back, and no values are lost.

Question 7

Converting to an ancestor class is what kind of conversion? (Widening or narrowing?)

Answer 7

Widening. An explicit cast is required to go the other direction.

Question 8

Will the following code throw?

Person person = new Person();
Employee employee = (Employee) person;

Answer 8

Yes, the underlying type is actually a Person not an employee.

Question 9

The is operator will returns true for an object if…

Answer 9

The type being checked is in the class hierarchy of the type being tested.

Question 10

What will an as operator return if the types are incompatible.

Answer 10

A null object.

Question 11

What are the three main methods for converting values?

Answer 11

Parsing methods
System.Convert
System.BitCoverter

Question 12

Parsing methods of conversion only apply to what kind of input and output?

Answer 12

Strings as input and primitive data types as output.

Question 13

How can you get some parsing methods to accept non-numeric characters?
Give some examples

Answer 13

System.Globalization.NumberStyles
AllowLeadingSign
AllowLeadingParenthesis
AllowDecimalPoint

Question 14

By default the decimal parser enables what NumberStyles?

Answer 14

Thousands and decimals (points)

Question 15

In C# U.S. formats always apply to what regardless of the locale?

Answer 15

Literal values

Question 16

What kind of rounding does ToIntXX, and ToUIntX use, and how does it work?

Answer 16

Banker’s rounding

Round to nearest integer, when tied go with nearest even.

Question 17

How would you do a conversion where you won’t know the type until runtime?

Answer 17

Use Convert.ChangeType(value,type)

Question 18

Once you have an array of bytes can you convert these into integers?

Answer 18

Yes, BitConverter has methods like ToInt

Question 19

Define Boxing and Unboxing

Answer 19

Boxing is converting a value type into an object or an interface that is supported by the value’s type. Unboxing is the converting a boxed value back into its original value.

Question 20

What are the two most common ways to engage interopperability?

Answer 20

COM Interop
Platform Invoke (PInvoke)

Question 21

Helper attribute for PInvoke to help manage data types

Answer 21

MarshallAs

Question 22

When C# does not understand a data type in a dll pulled in using COM, this type helps pacify the compiler.

Answer 22

dynamic type

Question 23

How does the dot net framework store chars?

Answer 23

UTF-16

Question 24

Are c# strings immutable?

Answer 24

Yes. When you think you are manipulating them, they are actually being created and assigned to the reference.

Question 25

Describe the intern pool and how It applies to strings

Answer 25

Each new string created is an entry into the intern pool. The intern pool holds a reference to each unique string. Since strings are I'm unable concatenating strings results in a lot of overhead, as each concatenation involves a new string creation and another entry into the intern pool.

Question 26

What is the purpose of StringBuilder.EnsureCapacity?

Answer 26

To allow the memory allocation up front, instead of having to do it later, essentially twice.

Question 27

A what point does StringBuilder become more efficient than concatenating strings.

Answer 27

Around 7 concatenations.

Question 28

What is the benefit/limitations of StringWriter vs. StringBuilder.

Answer 28

stringWriter is only for appending. It's faster while StringBuilder is more flexible. Also, StringWriter implements TextWriter.

Question 29

What is StringReader used for.

Answer 29

Reading strings sequentially. Plus StringReader implements TextReader.

Question 30

Can ToString be given formats?

Answer 30

Yes.

Question 31

Standard Numeric Format String: C or c

Answer 31

Currency

Question 32

Standard Numeric Format String: D or d

Answer 32

Decimal (Integer Types only)

Question 33

Standard Numeric Format String: E or e

Answer 33

Scientific Notation

Question 34

Standard Numeric Format String: F or f

Answer 34

Fixed-point

Question 35

Standard Numeric Format String: G or g

Answer 35

General (fixed-point or scientific, whichever is shorter.)

Question 36

Standard Numeric Format String: N or n

Answer 36

Number (with decimal and thousands separators)

Question 37

Standard Numeric Format String: P or p

Answer 37

Percent (multiplied by 100 and % added)

Question 38

Standard Numeric Format String: X or x

Answer 38

Hexadecimal (integer types only)

Question 39

Standard DateTime Format String: d

Answer 39

short date 3/14/2014

Question 40

Standard DateTime Format String: D

Answer 40

Long Date Friday, March 14, 2012

Question 41

Standard DateTime Format String: f

Answer 41

"Full" with short time | Friday, March 14, 2012 2:15 PM

Question 42

Standard DateTime Format String: F

Answer 42

"Full" with long time | Friday, March 14, 2012 2:15:16 PM

Question 43

Standard DateTime Format String: g

Answer 43

"General" with short time | 3/14/2014 2:15 PM

Question 44

Standard DateTime Format String: G

Answer 44

"General" with longtime | 3/14/2014 2:15:16 PM

Question 45

Standard DateTime Format String: m or M

Answer 45

Month/Day

Question 46

Standard DateTime Format String: t

Answer 46

short time 2:15 PM

Question 47

Standard DateTime Format String: T

Answer 47

long time 2:15:16 PM

Question 48

Standard DateTime Format String: y or Y

Answer 48

Year/Month March, 2014

Question 49

CLR

Answer 49

Common Language Runtime (CLR) A virtual machine that manages execution of C# (and other .NET) programs.

Question 50

composite format

Answer 50

composite format A format item used by String.Format to indicate how an argument should be formatted. The basic syntax is {index[,length][:formatString]}.

Question 51

immutable

Answer 51

immutable A data type is immutable if its value cannot be changed after it has been created. The String class is immutable. String methods that seem to modify a String, such as Replace and ToUpper, actually replace the String with a new value containing the modified contents.

Question 52

Unicode

Answer 52

Unicode is a standard for encoding characters used by scripts in various locales around the world. It enables a program to display English, Chinese, Kanji, Arabic, Cyrillic, and other character sets. The .NET Framework uses the UTF-16 encoding, which uses 16 bits to represent each character.