Introduction to Computer Programming CS 126 Lecture 3 Zeke Maier

Plan for Today • Questions • Administrivia • Data Types and Expressions • Assignment

Questions • Steve Jobs – Health?

• Products?

– iPod – iPhone – iTunes – MacBook • Macworld – iTunes Store selling DRM free music

Administrivia • http://students.cec.wustl.edu/~ejm3/ – TAs!

– CEC accounts – Lab assignments – Readings

Data Types • Everything in Java has a type – type: “kind of thing” • Primitive Types – int: Integer number: 5, 10, 15 – double: Decimal number: 5.15, 10.25

– boolean: true or false – String: a string of characters: “Hello World”

Expressions • Expression: anything that has a value – infix expression syntax • operators between operands • Order of operations – Evaluate left to right under the rules 1. Negation (

-

) 2. Multiplication(

*

), Division(

/

), & Modulus(

%

) 3. Addition(

+

), Subtraction(

-

)

Expression Trees • Evaluated left to right and bottom to top

+ *

% 8 5 18 5

String Concatenation •

+

operator will combine strings together – Other primitive values will be converted to strings when concatenation occurs Boolean Expressions • Expressions that evaluate to

true

or

false

•

&&

and operator • • •

!

|| ==

or operator not operator equals operator

Variables • A symbol which can hold a value of a particular type int age; String myName; double cars; • Assign a value of a variable int age = 24; String myName = “Zeke”; double cars = 0.5; • Assign the value of an expression to a variable double money = 45.50 - (3 * 1.50);

Assigning New Values • Variables can be reassigned a new value int age = 24; age = 25; int age = 24; age = age + 1; •

final

keyword forces variable to retain initial value • final variables, called constants, have all uppercase names final int AGE = 24; AGE = 25; //Error

Composition • Combining small blocks of code – How could we compose these three statements into a single statement?

int age; age = 24; System.out.print(age);

Naming Abstraction • Giving names to values: using variables – What are some advantages?

• Choose meaningful names for variables!

Circle Area Example

Assignment • No Class Monday • Readings – Wednesday • AD Chapter 2, Chapter 7: 7.8 - 7.10

• KG Notes