CIS 199 Final Review

New Material

Classes Reference type

NOT a value type!

Can only inherit from ONE base class

Properties Class member Holds a piece of data, information within an object Accessors: get, set

Can use auto-implemented when validation is not required If need validation, must create own backing field (instance

variable) and write own get and set accessors Read-only property – only has get, no set (no public set, at least)

Controllable scope

readonly Can make an instance variable readonly Initial value will be established in constructor After value is set, it may not change again

Inheritance Extend, Expand an existing class Specialization Generalization “All students are a person, but not all persons are a student” Derived class “IS-A” base class

Student IS-A Person

Even if no base class is specified, one will be provided Object This is where method ToString was originally defined

Protected vs PrivateWhat is the difference between Protected vs Private?

Protected vs Private Private-The type or member can be accessed only by code

in the same class Protected -The type or member can be accessed only by

code in the same class, or in a class that is derived from that class.

Polymorphism

Complicated Concept An object’s ability to take on, become different forms

Child classes take on properties of parent Objects may be treated as base class

Students can be treated as a person Keywords of note:

“override” – New implementation of a member in a child class that is inherited from base class

“virtual” – Class member that may be overridden in a child class “abstract” – Missing or incomplete member implementation.

MUST be implemented by child classes // More a 200 concept

Abstract Classes

Generic class Provides some members, some information CAN NOT be created directly

Meaning direct instantiation is illegal

Serves as a common “base” for related objects

Test 01 Material

Computer Hardware Central Processing Unit (CPU)

Brains Operations performed here

Main Memory (RAM) Scratchpad Work area for programs, process, temporary data

Secondary Storage Hard drive Flash drive CD, DVD

Input, Output Devices Input

Takes data IN Keyboard, Mouse, Game Controller, Microphone

Output Pushes, places data OUT Display, Speakers, Printers

Programs and Digital Data Programs

Operating Systems. Microsoft Office, Web browsers Instructions read by CPU and processed

Digital Data 1’s 0’s …forms binary (base 2)

Built-In Types

Formatted Output Placeholders Letter codes – C, D, F, P Precision Field width

Console.WriteLine(“x = {0,-10:F2}”, x);

Operators ++, --

Postfix vs Prefix

int x = 5;

int y;

y = x++; vs y = ++x; Shorthand operators

+=, -=

Integer division

1/2 == 0

1.0 / 2.0 == 0.5

10 / 3 == 3, 10 % 3 == 1 = vs ==

Properties Exposed “Variables” or accessible values of an object Can have access controlled via scope modifiers When thinking of properties: Values and definitions “get” – Code to run before returning a value “set” – Code to run before updating a value

Can be used for validation and other processing actions “value” is a keyword in “set”

Methods Actions, code to be executed May return a value, may take value (not required) Can be controlled via scope keywords Can be static // Different example

Scope “private” – Can only be accessed by the class, object itself “protected” – Can only be accessed by the class, object, or

any child classes, objects “public” – Available access for all

Named Constants AVOID MAGIC NUMBERS! Allows for reference across similar scope Change once, changes everywhere // ALL CAPS

Conditional Logic if(expression)

If ‘expression’ is true If not true, skipped

else if(expression) Can be used to ‘chain’

conditions Code runs if ‘expression’ is

true

else Code to execute if

‘expression’ false

Statements can be nested

Relational Operators >

Greater than <

Less than >=

Greater than OR equal to <=

Less than OR equal to ==

Equal to !=

NOT equal to

X > Y

X >= Y

X < Y

X <= Y

X == Y

X != Y

Operator Precedence (Highest) ++, --, ! * / % + - < > <= >= == != && || = *= /= %= += -= (Lowest)

Comparing Strings, Chars

You can use ==, !=

You cannot use >, >=, <, <=

You SHOULD use: String.Compare(s1, s2)

s1 > s2 Returns positive Number

s1 = s2 Returns zero

s1 < s2 Returns negative number

Compares the unicode value of EACH character

Test 02 Material

Basic GUI Example

Textboxes, labels, buttons, checkboxes, radiobuttons, panels, groupbox

Event handler

Loops for

“For a given value X, while X is true, modify X…”

while “While X is true…”

do – while “Do these tasks, while X is true…”

foreach “For every X in this set of Y do the following…”

for Example

while Example

do while Example

foreach Example

Key Loop Details Loops are NOT guaranteed to execute at least once!

…only exception is ‘do while’ Pretest vs posttest, or entry vs exit test

‘for’ loops require a variable, condition, and ‘step’ instruction ‘while’, ‘do while’ loops require a boolean expression ‘foreach’ loops require a collection of items

Arrays

Indefinite repetition – sequential search, sentinel control, validation loop

Nested loops

Output

Methods Actions, code to be executed May return a value, may take value (not required) Can be controlled via scope keywords Can be static

Methods & Modularizing Your Code Methods

Break out ‘steps’ Easier to test Easier to visualize

Top Down Design

Arrays

Arrays

Sample Questions onBlackboard Wiki

What does ‘WYSIWYG’ stand for? What You See Is What You Get

What is the difference between a high-level and a low-level language? Low-Level

Little to no ‘abstraction’ from the hardware or computer “Close to the hardware” Simple, but Difficult to use Machine code, assembly, C (in some cases)

High-Level Very strong ‘abstraction’ from the hardware or computer “Far from the hardware” Easier to use, abstraction adds complexity C++, Java, C#, Python

How is the lifetime of a FIELD different from a lifetime of LOCAL variable?

Fields are members of their containing type

Fields can be used everywhere with appropriate scope

Local variables can be used only in their “local” environment

What two things does a variable declaration specify about a variable?

Type Identifier

TYPE IDENTIFIER

Describe ‘&&’ and ‘||’ and how they work.

&& (AND) Returns true if conditions are

ALL true “If you do well on the test

AND the quiz, you will earn a great grade!”

|| (OR) Returns true if ANY

conditions are true “You can run a mile OR walk

two miles (possible do both!)” Both short circuit

Why is ‘TryParse’ more effective than ‘Parse’?

Less code No try / catch required

What is the difference between a SIGNED an UNSIGNED int?

What is the difference between syntax errors and logic errors?

Syntax Errors – Errors that prevent compilation or other factors that prevent successful compilation string myString = string.Empty; // Won’t compile, syntax error

Logic Errors – Errors that occur during runtime, such as incorrect comparison or other unexpected behavior If(grade > 60) { Code if grade is F } // Incorrect operator used

What are the “Five logical units”?

CPU – Processing, instructions Memory – Scratch pad, working space (Temporary) Secondary Storage – Hard drives, storage (Long term) Input – Keyboards, Mice, Controllers Output – Monitors, Speakers, Printers

Explicit type conversion? Why and how?

Variables must be used for a single type never change Move from one type to another, must cast EXPLICIT cast / type conversion

Aware of information loss

Write a code fragment that will display “Good Job” when int variable score is 80 or more, “OK” when score is 70 – 79, and “Needs Work” for any score under 70.

Write a code fragment that will apply a 10% discount to the value in double variable total when int variable numItems is 5 or more and int variable zone is 1, 3 or 5.

The ‘switch’ statement can replace nested if/else. But under what conditions?

When matching on a specific… Value Type Enumeration …other data Doesn’t work for floating point types

What does a ‘break’ statement do in a loop? It stops (BREAKS) loop execution Code continues, no further loop iterations

Example:

switch (comboBox1.SelectedItem.ToString())

{

case "A":

class_one_textBox = int.Parse(textBox1.Text); grade = 4.00 * class_one_textBox;

break;

case "A-": class_one_textBox =int.Parse(textBox1.Text); grade = 3.67 * class_one_textBox;

break;

What does a ‘continue’ statement do in a loop?

Goes to the next iteration CONTINUES loop execution, by skipping current iteration This is only time a for loop would behave differently than a

while loop

What are preconditions and postconditions for a method?

PRECONDITIONS Conditions that MUST be TRUE before method execution

POSTCONDITIONS Conditions that WILL be TRUE after method execution

What is the difference between a void method and a value-returning method?

VOID Method Returns nothing! …a void return.

Value-Returning Returns a value! …that’s not a void return.

Compare and contrast the use of pass by value against pass by reference, using key word ref versus pass by reference using keyword out.Pass by Value

Passes a copy of the value Not the object itself

Pass by Reference Passes the actual object itself

‘ref’ Causes a pass by reference on a variable

‘out’ Is used to reference a variable that the method will update

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