lecture 2 fundamental data types. variable declaration
TRANSCRIPT
All Numeric Types have Finite Ranges
0 1 1 1 1 1 1 0
0 0 0 0 0 0 0 1
0 1 1 1 1 1 1 1
0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1
value is 128but the leading 1 indicates negative value
value is 127
Increment and Decrement Operators
Notice: In this course, we will NOT be using increment and decrement operators in regular assignment statements. (More on this later.)
When is "=" not Equal to "Equals"?
In Java (and most other programming languages) the symbol = means assignment.
X = X + 1 "X is assigned the value X + 1
X = X + 1ALU
Arithmetic LogicUnit
ADD
LOAD
STORE
Ingredients
1 stick butter 1/2 cup sugar 1 egg 1 teaspoon vanilla extract 1/2 teaspoon salt 1 3/4 cups all-purpose flour
Directions
Mix the butter and sugar until light and fluffy. Beat in the egg, then vanilla and salt. Mix slowly while gradually adding the flour. Do not overmix. Shape into a 1-inch-thick disk, refrigerate for at least 2 hours. Heat oven to 350° F. Roll the dough ¼ inch thick, and cut the dough into shapes. Place 1 inch apart on prepared baking sheets, sprinkle with sugar. Bake until the edges just begin to brown, 12 to 15 minutes. Transfer to cooling racks.
Sugar Cookie Recipe
Parameters
pi = 3.1415926 radius area
Actions
Read in the radius. Compute the Area using the formula:
Display Area.
Circle Area Algorithm
Computer Algorithms can be simpler than a recipe for sugar cookies. ;-)
Getting Input from the User
We can use the Scanner software package provided as part of java.util to get information typed on the keyboard. Some of the methods provided in Scanner are:
Convert Seconds to Minutes and Seconds
Get total seconds from user.
Calculate number of whole minutes.
Calculate number of remaining seconds.
Display results.
Numeric Type Conversions
Java performs automatic type conversion in mathematical expressions. For example, when an integer and a floating-point value are multiplied, the integer is promoted to a floating-point value.
We can override the default type conversions by specifying the type of each parameter.
9
2+i3𝜋
25
Oh great! Here come yourfriends, the odd couple.
For starters, they're a coupleof squares.
Why can't you keep it real?
I can't imagine whyyou don't like them.
As usual, you're being irrational.
Why do you insist on running on forever?
Conflicting Data Types
Types of Programming Errors
syntax errors - This type of error prevents the compilation of the program into an executable binary or into bytecode.
runtime errors - This type of error prevents a running program from completing its normal execution.
logic errors - With this type of error a program can complete its execution normally but the results obtained will be incorrect.
• easiest type of error to detect• relatively simple to correct
• can be data dependent• don't always occur (consider the divide-by-zero error)
• most difficult to detect (especially when they are intermittant)• amenable to unit testing and other SW engineering methods• can never be completely eliminated in large programs
Algorithms are like Recipes
The Input-Process-Output Design Pattern
Comments help make code understandible
All Numeric Data Types have finite ranges
Values can be converted from one data type to another
Floats and Doubles approximate Real Numbers
java.util Scanner methods support user input
Understanding Assignment Operators
Increment and Decrement Operators
Introducing Processing.org
Unicode and ASCII Code
Escape Sequences
Programming Errors
Input and Message Dialogs
Chapter 2 Summary