1. COMP 110: Introduction to Programming
Tyler Johnson
January 21, 2009
MWF 11:00AM-12:15PM
Sitterson 014

2. Announcements Lab 0 due tomorrow by midnight Submit via blackboard
Michele Weigle - COMP 14 - Spr 04
Announcements
Lab 0 due tomorrow by midnight
Submit via blackboard 2

3. Questions?

4. Today in COMP 110 Objects and Classes Algorithms and Pseudocode
Michele Weigle - COMP 14 - Spr 04
Today in COMP 110
Objects and Classes
Algorithms and Pseudocode
Variables & Operations
Programming Demo
Vending Machine Change 4

5. Object-Oriented Programming
What are objects?
Entities that can represent real-world things or abstractions
E.g. Cars, houses, books, System.out (abstract)
Objects perform or have actions performed on them
car.start()
house.clean()
book.read()

6. Object-Oriented Programming
What is object-oriented programming?
Programming methodology where programs are composed of a collection of objects that can act alone or interact with one another
Example
A race car simulation program might have car, driver, racetrack, and onlooker objects
A driver might ‘drive’ a car object
An onlooker object might ‘boo’ a driver object

7. Object Attributes Objects have attributes Example
A car object might have the following attributes
Make
Model
Year
Owner
Location
The set of an object’s attributes is called its state

8. Object Actions
Objects perform actions, or have actions performed on them
Example
A car object might allow the following actions
Accelerate
Brake
Sell
Start

9. Object Actions Performing actions on a object can change its state
Example
If we sell a car, we change its owner
If we accelerate the car, we will change its location

10. Classes
A Class describes a general template for creating a certain kind of object
Example
We have two car objects
One is a 2000 Toyota Camry owned by John Doe
A second is a 2001 Ford Focus owned by Samantha Smart
While the two car objects are different, they are both types of cars and have the same type of attributes
Both cars are thus members of the Class Car

11. Classes and Objects Class Car Camry object Focus object Make Model
Year
Owner
Location
Camry object
Make = Toyota
Model = Camry
Year = 2000
Owner = John Doe
Location = Garage
Focus object
Make = Ford
Model = Focus
Year = 2001
Owner = Samantha Smart
Location = School

12. Algorithms What is an algorithm?
Michele Weigle - COMP 14 - Spr 04
Algorithms
What is an algorithm?
A set of instructions for solving a problem 12

13. Algorithm Example How to make a peanut butter and jelly sandwich?
Michele Weigle - COMP 14 - Spr 04
Algorithm Example
How to make a peanut butter and jelly sandwich?
Get two slices of bread
Get some peanut butter
Get some jelly
Get a knife
Spread peanut butter on the first slice of bread
Spread jelly on the second slice of bread
Put the two slices of bread together 13

14. Michele Weigle - COMP 14 - Spr 04
Pseudocode
Combination of code and English used to express an algorithm before writing the algorithm into code
Useful in planning out programs before you actually write them 14

15. Algorithm Example 2
How to compute the total cost of all the groceries in your shopping cart?
Simple, just start with the number 0 and add the cost of each item one by one.
Let’s look at how we might describe this in pseudocode

16. Michele Weigle - COMP 14 - Spr 04
Algorithm Example 2
Computing the total cost of groceries in pseudocode
total = 0
for each item in the cart
total = total + (cost of that item)
At the end of the algorithm, “total” is the total cost of all items in the cart 16

17. Variables Used to store data in a program Example
Think of it is a container for a value
Example
myVariable = 6;
Set the value of “myVariable” to 6
Can change value throughout program
myVariable = 8;
The value of “myVariable” is now 8

18. Variables Name of a variable is called its identifier
Choose variable names that are meaningful!
Example
a = a + b;
No one will know what these variables mean
accntBalance = accntBalance + deposit;
Is much better

19. How to use Variables Declare a variable Assign a value to the variable
Change the value of the variable

20. Variable Declarations
Tells the computer what type of data the variable will hold
Allocates space in memory for the data
Examples:
int count, score, myInt;
char letter;
double totalCost, ratio;

21. Syntax Set of grammatical rules in a language
Simple syntax for English sentences
Subject Verb Object.
E.g “I won the game.”
Syntax for variable declarations in Java:
Type Variable_1, Variable_2, …;
Examples:
int count, score, myInt;
char letter;
double totalCost, ratio;

22. Variables and Memory A variable corresponds to a location in memory
variable n1
Use this cell to store the value of n1
Prevent this cell from being used by other variables later
main memory

23. Type What kind of value the variable can hold Two kinds of types
Michele Weigle - COMP 14 - Spr 04
Type
What kind of value the variable can hold
Two kinds of types
Primitive type - indecomposable values (single number or letter)
int, double, char, boolean
Class type - objects with both data and methods
Scanner, System
We have seen these class types in the FirstProgram code 23

24. Four Kinds of Primitive Types
Integer types
byte, short, int, long
Represent whole numbers such as 0, 5,
Floating-point types
float, double
Represent numbers with some fractional component such as 1.01, , 0.0
Character
char
Represents a single character such as ‘A’, ‘;’, ‘8’
Boolean
boolean
Represents a single bit (on or off, true or false, 1 or 0)

25. Java Primitive Types Type Name Kind of Value Memory Used
Range of Values
byte
Integer
1 byte
-128 to 127
short
2 bytes
-32,768 to 32,768
int
4 bytes
-2,147,483,648 to 2,147,483,647
long
8 bytes
-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
float
Floating-point
± x to ± x 10-45
double
± x to ± x
char
Character
0 to 65,535
boolean
1 bit
True or False (0 to 1)
Size of this class? Population of the world? mass of Earth = × 10^24 kilograms, mass of the sun = × 10^30 kilograms. Character ‘!’. Whether this class is fun?

26. Variables and Memory
When declaring a variable, a certain amount of memory is assigned based on the declared primitive type
int age; double length; char letter;
main memory

27. Variable Declaration
Why is it important to tell the computer the type of the data?
Different types of data take up different amounts of space in memory
Different types of data may allow different operations
We can add two numbers, but does it make sense to add two letters?

28. Variable Declarations
For now, declare all your variables inside main
public class ExampleProgram
{ public static void main(String[] args) {
int count;
double average; … }

29. How to Name Variables Use a combination of
Michele Weigle - COMP 14 - Spr 04
How to Name Variables
Use a combination of
Letters, digits (0-9), underscore (_)
First character cannot be a digit
Java is case sensitive
“myVariable” & “myvariable” are considered different identifiers 29

30. Example Variable Names
Legal names
inputStream, my_Grade, my_Grade2
Illegal names
bright*, power-hour, 7eleven

31. Variable Names Exercise
pinkFloyd
michael.bolton
the_cure
b3atles
kenny-G
311
Legal?
Yes No

32. Keywords Reserved words with predefined meanings
Michele Weigle - COMP 14 - Spr 04
Keywords
Reserved words with predefined meanings
if, else, return, new, …
See the inside cover of the textbook for full list
You cannot use a keyword as a variable name
int if;
will not compile
int ifThen;
Is ok 32

33. Assignment Statements
Change a variable’s value
Syntax:
variable = expression;
Example:
sleepNeeded = 8;
sleepDesired = sleepNeeded * 2;
‘=’ sign is called the assignment operator

34. Behind the Assignment Statement
variable = expression;
CPU calculates the value of the expression
Writes the value to the memory location of the variable
sleepDesired = sleepNeeded * 2;
Get the current value of sleepNeeded from its memory location
Calculate sleepNeeded * 2
Assign the result to the memory location of sleepDesired

35. Assignment Statement
A variable can occur on both sides of an assignment statement
Example
count = count + 10;

36. Variable Initialization
You need to give variables an initial value before you use them
Otherwise you may observe unexpected behavior
int count;
count = 1;

37. Variable Initialization
You can also initialize variables directly in the declaration
For example
int myVar;
myVar = 0;
Is equivalent to
int myVar = 0;

38. Variable Initialization
Multiple variables can be declared and initialized simultaneously
int grade0 = 95, grade1 = 89, grade2 = 71;
For example, this is a student who stopped paying attention during lectures in COMP110, let that be a lesson to you.. ;]

39. Arithmetic Operators The usual suspects Addition (+) Subtraction (-)
a + b
Subtraction (-)
a - b
Multiplication (*)
a * b
Division (/)
a / b

40. Division Operator
The division operator (/) behaves differently depending on the data types used!
Example
9 / 2 = 4
Truncation when used with integers
9.0 / 2 = 4.5
Maintains fractions when used with real numbers

41. Division Operator Examples
3 / 2.0 =
3 / 2 =
6 / 3 =
6.0 / 3 =
11. / 2 =
1.5 1 2
2.0
5.5

42. Remainder Operator
The remainder or modulo operator (%) gives the remainder when one whole number is divided by another
Example
i = 10%4; //the value of i will be 2
j = 6%3; //the value of j will be 0
k = 17%6; //the value of k will be 5

43. Remainder Operator
The remainder operator can be used to determine if a number is even or odd
Given any integer n, n%2 will produce either 0 or 1
If n%2 equals 0, n is even
If n%2 equals 1, n is odd

44. Review
You should now
Have a better understanding of objects and classes
Have a good idea of what an algorithm is
Be able to write a basic Java program that performs simple arithmetic

45. Vending Machine Change
Problem
Given an amount of change from 1…99, determine the number of quarters, dimes, nickels, and pennies that equals that amount of change
Example:
57 cents would be dispensed as
2 quarters, 0 dimes, 1 nickel, and 2 pennies

46. Programming Demo Vending Machine Change Steps Pseudocode Programming
Testing/Debugging

47. Designing the Algorithm
How do we know that 57 cents is 2 quarters, 0 dimes, 1 nickel and 2 pennies?
First we used as many quarters as we could (2)
That leaves 7 cents
Second we used as many dimes as we could (0)
Still left with 7 cents
Third we used as many nickels as we could (1)
That leaves 2 cents
Lastly we used the remaining amount as pennies (2)

48. Vending Machine Change
Pseudocode
Ask user for the amount of change
Determine the amount in quarters
Subtract the value in quarters from amount
Determine the amount in dimes
Subtract the value in dimes from amount
Determine the amount in nickels
Subtract the amount in nickels from amount
Set the number of pennies to the remaining amount
Output the result

49. Vending Machine Change
Programming

50. Vending Machine Change
Testing/Debugging

51. Program 1 Tip Calculator Due Feb 4th START EARLY!
Posted on course website
Due Feb 4th
START EARLY!

52. Friday Recitation Bring Lab 1 Laptops (fully charged) Textbook
Any questions you may have about Program 1