MT1

Question 1

Purpose of top-level statements?

Answer 1

write smaller programs without the use of the main method

Question 2

How to write top-level statements

Answer 2

1. “using” directives (optional)
   ex. using System; using System.Collections.Generic;
   (compiler automatically adds set of “using” directives” based on project type)
2. Statements (what we would write in main method)
   ex. Console.Writeline…
3. More type / namespace declarations (optional)
   - used when we have user-defined classes etc.

Question 3

What happens to a top-level statement?

Answer 3

compiler will put statments (not written in main method) into an auto-generated method / class

if methods are used to write top-level statements, then they become local functions

at most one file in C# project can have top-level statements

Question 4

What makes software high quality?

Answer 4

1. correct (safe from bugs)
2. comprehensible (readable, understandable)
3. changeable (ready to change)

Question 5

What is a type

Answer 5

set of values (data) and the operations permitted on the values

Question 6

Two naming conventions

Answer 6

PascalCasing –> class + method
camelCasing –> local variables + fields

Question 7

What is a constructor?

Answer 7

method used to initialize objects whenever an instance of the class (both have same name) is created

ex. when class Date is instantiated, constructor Date will set up an int type to create the numerical value of said Date

Question 8

What does “private” mean

Answer 8

protects types from being manipulated outside of the class it is in.

Question 9

Value vs Reference type

Answer 9

Value types –> need 1 allocated memory space to store data
ex. int x = 5;

Reference type –> stores reference to some other memory location where actual data is stored
ex string str = “hello” (str is immutable because it only references a memory locattion)

Question 10

Explain the concept of Stack and Heap

Answer 10

Stack and Heap –> regions of memory to store data

Stack–> stores value types + reference type (only the reference), LIFO data structure

Heap –> stores actual data of reference type

Question 11

What is a class?

Answer 11

type that stores logically related data + functions

a way to create + define new types and a set of values + operations associated with that type

contains:
data members –> variables
function members –> operations

Question 12

What is a Class: Field?

Answer 12

stores data
a variable (of any type) that is a member of a class

PascalCasing for static public + protected fields
otherwise camelCasing

Question 13

What is a Class: property?

Answer 13

member that represents data
(looks like a field but it does not necessarily allocate memory for data)

name set of two methods (accessors):
set + get

Question 14

What is a method?

Answer 14

Block of code that can be executed / invoked
( do not use void to indicate that method doesn’t take parameters; simply use () )

Question 15

What are local variables

Answer 15

holds temporary data within scope of a method (doesn’t exist outside of a method)

Question 16

Difference between Private and Public Access Modifiers

Answer 16

Private members –> accessible within class in which they are declared (default access level)

Public members –> accessible to other objects in program

Question 17

What does the following code do?

Console.WriteLine(message + “ “ + name)

Answer 17

Appends the data for message, appends a space, and appends the data for name

Question 18

What happens to the string if a code below is compiled:

Console.WriteLine($”{message1.ToUpper()}”);

Answer 18

prints in ALL CAPS

BUT
b/c strings are immutable, a new string data is created that has the same string but modified.

Question 19

What is String Builder

Answer 19

provides a mutable alternative to string
(uses namespace: System.Text)

ToString –> convert to string
Append –> adds value
Clear , Remove, Insert etc.

Question 20

What is encapsulation?

Answer 20

information hiding
ex. declaring fields to be private

advantage: hiding details allows them to be changed later without changing the entire system

Question 21

What is Inheritance?

Answer 21

types can be derived from other types (types can be subtypes)
ex. all types derived from System.Object type

Question 22

Polymorphism

Answer 22

ability of object to take on many forms
ex. (supertype can refer to subtype object)

Question 23

What is method overloading?

Answer 23

allows us to create multiple implementations of method with same name

ex.

public int Add(int a, int b, int c)
{
return a + b + c
}
public int Add(int a, int b)
{
return a + b
}

Question 24

What is an array?

Answer 24

set of uniform data elements represented by a single name
- size cannot be changed

int[] array = {1, 2, 3} ;
char [] array = “string”

Question 25

What are lists?

Answer 25

data type representing an ordered sequence of elements that can be accessed by index
- can add / remove elements

• initialize via using directive:
  ex. using System. Collections. Generic;

List<T> (where T can be any type
List<int> numbers = new List <int>();
List <char> characters = new List <char> ();</char></char></int></int></T>

Question 26

Methods of List <T> class</T>

Answer 26

list.Add –> adds elements to end of list
Remove –> removes first occurence of specified object from list
Insert –> inserts elements into list at specified index
Clear–> removes all elements
ToArray –> copies elements of list to a new array
list.Count –> gives length of list

Question 27

What are math methods

Answer 27

static methods used to compute mathematical calculations
ex.
Math.Cos()
Math.Sqrt()
Math.Abs()
+ , -, / , *,

uses System namespace

Question 28

What is overflow?

Answer 28

when data inputted / calculated is larger/ smaller than the range (out of bounds of type range)

Question 29

What is BIgInteger?

Answer 29

struct used to represent an arbitrarily large signed integer
** creates immutable objects**

using System.Numerics

can be instantiated:
1. using constructors:
BigInteger num - new BigInteger (123)
2. as a numeric type (for integrals)

Question 30

What happens when this code is compiled:

int x = 2_000_000;
BigInteger y = x * 2;

Answer 30

Overflow occurs because x and 2 are integers.
When multiplied they create a value of type int that exceeds the range

to fix:
BigInteger.Multiply(x, 2)
or
cast x and 2 to be Big Integers

Question 31

What is static checking
ex.
int x = 13;
if (x == false) { … }

Answer 31

bug found automatically before program even runs

Can detect:
syntax errors (missing paranthesis)
wrong names (Math.sine(2)
wrong numer of arguments (Mat.Sin(2,3))
Wrong argument types
Wrong return types

Question 32

What is dynamic checking
ex.
int x = 12, y = 0;
Console.WriteLine(x/y)

Answer 32

bug found automatically during runtime
- sometimes compiler must run in order for language to see what variables stand for etc.

Can detect:
- illegal argument values (x/y when y = 0)
- unrepresented return values (when the value of return is not related to its type)
- out-of-range indexes (run time index being too-large)
- calling a method on a null object reference

Question 33

What happens in “no checking”

Answer 33

language doesn’t help with finding error

Question 34

What is readonly and how is it used for defensive programming?

Answer 34

keyword used to indicated that a field can only be assigned at the time of declaration / in a constructor of that class.

Question 35

What does the const keyword do?

Answer 35

declares a constant local / field

• can only be initialized at declaration (immutable afterwards)

Question 36

What happens when this code is compiled?

class Age
{
readonly int year;
public Age (int year)
{
this.year = year;
}
void ChangeYear()
{
year = 1967;
}
}

Answer 36

Compiler error
–> year has been initialized due to the keyword “readonly” which only lets the data to be assigned in a constructor

Question 37

Function of “this” keyword

Answer 37

used to quality class members that have the same name as the parameters

int Quadratic Equation(int a, int b, int c)
{
this.a = a;
this.b = b;
this.c = c;
}

Question 38

What is a Queue and what are its operations?

Answer 38

FIFO structure

enqueue –> add item at end
dequeue –> remove item at front

Question 39

What do the paranthesis when instantiating a data abstraction do?

Queue<string> numbers = new Queue<string>();</string></string>

Answer 39

used for constructors
–> creates an empty data abstraction

Question 40

What are operations for Stack data abstraction?

Answer 40

push –> add elements to top of stack
pop –> remove elements at top of stack

Question 41

What is a Dictionary <Tkey, Tvalue>

Answer 41

data type that holds a colletion of “key-value” pairs (key, value)
ex. collection of all (country, capital city) pairs

Question 42

What is a set?

Answer 42

datatype in which we can add / remove elements + check if an element is in a set

–> unordered + do not contain duplicates

Question 43

what is .NET

Answer 43

takes source code file and produces intermediate output file (assembly)

• code in assembly is an intermediate language