cis 199 final review. new material structures value type not a reference type! used to...

CIS 199 Final Review

New Material

Structures Value type

NOT a reference type!

Used to encapsulate small groups of related variables

Classes Reference type

NOT a value type!

Like a structure, but far more sophisticated, modern Can only inherit from ONE base class Can inherit from MANY interfaces

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

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

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

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

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

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

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)

Detailed from:http://msdn.microsoft.com/en-us/library/2bxt6kc4%28v=vs.100%29.aspx

Comparing Strings 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

Exceptions andException Handling Exceptions are…

“Exceptional” events Unexpected events, errors during runtime Unhandled exceptions? Stack trace and application death

Handled with try/catch/finally blocks Try block “attempts” to run the code in question Catch block handles the exception(s) that may occur Finally block, optional, always executes

Test 02 Material

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’

‘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 Lists Generic Collections

Files OpenFileDialog

Used to load file from location

SaveFileDialog Used to select file save location

BOTH very User friendly!

OpenFileDialog

OpenFileDialog

SaveFileDialog

SaveFileDialog

Random Numbers in C# Provided from: System.Random Is ONLY pseudo-random

Produces a finite set of values with equal probability Not truly random, follows a mathematical algorithm

Created with OR without seed value Common methods used:

Next() Next(int) Next(int, int) NextDouble()

Creating and using aRandom Object

Usage & Expected Resultsof Random Methods

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

Methods &Modularizing Your CodeExample

Arrays

Arrays

Sample Questions fromBlackboard 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!)”

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 striing 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

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

What does a ‘continue’ statement do in a loop? Goes to the next iteration CONTINUES loop execution, by skipping current iteration

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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