Type System

Question 1

What is a type?

Answer 1

Type defines a blueprint for a value.

Question 2

What is a predefined type?

What are some predefined types?

Answer 2

Predefined is a type that is specially supported by the compiler. In C#, predefined types are recognized with a C# keyword.
Examples of predefined types are: int, string, bool
https://stackoverflow.com/questions/13464641/c-sharp-predefined-types-vs-primitive-types/46866599#46866599

Question 3

How is data created?

Answer 3

Data is created by instantiating a type.

Question 4

How is a predefined type instantiated?

Answer 4

Simply by using a literal, such as 12 or “Hello, world”

Question 5

How is a custom type instantiated?

Answer 5

Using “new” operator.

MyType instanceOfType = new MyType();

Question 6

What comprises value types?

Answer 6

Most built-in types (all numeric types, char and bool types) as well as custom struct and enum types.

Question 7

What comprises the reference types?

Answer 7

Class, array, delegate and interface types. String type is a reference type as well.

Question 8

What does a reference-type variable contain?

Answer 8

A reference-type variable contains a reference to an object that contains the value.

Question 9

What is the difference between reference and value types in regards to them containing null value?

Answer 9

Reference types can be assigned null value which means that they point to no object. Value types cannot ordinarily have a null value. (Exception: nullable value types)

Question 10

Are all types from System namespace predefined in C#?

Answer 10

No. System namespace contains many types that are not predefined by C#. For example DateTime.

Question 11

Is System.DateTime type predefined in C#?

Answer 11

No.

Question 12

List 4 type categories in C#.

Answer 12

1. Value types.
2. Reference types.
3. Generic type parameters.
4. Pointer types.

Question 13

How is anonymous type created?

Answer 13

To create an anonymous type use “new” operator with the object initializer.

var v = new { Amount = 108, Message = “Hello” };

In this case “Amount” and “Message” are user defined object properties and their type will be derived by the compiler.

Question 14

Are methods and events allowed in anonymous types?

Answer 14

No. Only properties are allowed to be defined in the anonymous type.

Question 15

What is accessibility level of properties in an anonymous type?

Answer 15

Properties of an anonymous type are read-only.

Question 16

Can a static class contain instance variables? Here is an example:

static class MyClass
{
    int myIntVar = 3;
}

Answer 16

No. 
All data and function members of a static class must be static.

Question 17

How many bytes will the following Struct occupy in memory?

struct MyStruct{
int x;
int y;
}

Answer 17

8 bytes. 4 bytes for each integer and no overhead. Value type instances occupy precisely the memory required for their fields.

Question 18

What information is stored in the overhead of the reference type instance?

Answer 18

1. The key to object’s type.
2. Object’s lock state.
3. Whether the object has been flagged by garbage collector.

Question 19

What type does a compiler infer a variable to be if it is a number with a decimal point?

Answer 19

The number with a decimal point is always inferred to be a double type by a compiler.

Question 20

What is the largest number that int can hold in C#?

Answer 20

2^31 - 1. int has 4 bytes to store its value but 1 bit is reserved for a sign value of a number.

Question 21

Which real number type is typically used for financial calculations where base-10 accurate arithmetic is required?

Answer 21

decimal

Question 22

How is hexadecimal value denoted in C#?

Answer 22

Hexadecimal value is denoted with “0x” prefix. For example: long x = 0x7F;