CSC 142/Chapter 2

Chapter 2: Primitive Data and Definite Loops

Sections:

2.1 Basic data concepts

2.2 Variables

2.3 The for loop

2.4 Managing complexity

2.5 Case study: Hourglass figure

Note: this chapter has two halves. The first half examines expressions, particularly for numerical data and variables. The second half examines control structures, used to perform repetitive actions.

The goal here is pattern-finding - what repeated actions will lead to the desired outcomes? This loop will cover definite loops (loops that repeat a predetermined number of times). Next chapter will cover indefinite loops.

Section 2.1: Basic data concepts

2.1 Definitions

Definitions:

• Data type
• Expression
• Evaluation
• Operator
• Precedence
• Casting

2.1 Material

Java primitive types:

• int
• double
• char
• boolean

Why important? because computers represent data and numbers in memory, and we need to understand how (rules)

How we input data and operations:

• literals (literal values, 2.19)
• expressions (assembling stuff, related by operators)

Operators:

• Mix of computer science and math
• Operators mean, performing a set of tasks (or, a task)
• Some operators require 2 things, e.g., 2+3
• Some operators require 1 thing, e.g., inverse(A) or d/dx( x^2 )

Literals

• Different data types
• Decimals vs integers (especially with operations)
• Booleans: true/false (keywords)

Arithmetic

• Division weirdness
• Remainder operator
• Goldfish analogy - small memory capacity - 2 digits - what happens after 99? start over

Precedence and order of operations

• Grammar connection
• Be explicit in what you're asking computer to do

Casting and file types

• can deal with int/float differences by casting
• Again, be explicit: (int)( ......... )

Section 2.2: Variables

2.2 Definitions

Definitions:

• Variable
• Declaration
• String concatenation
• Increment/decrement

2.2 Materials

You have to declare it available in order to use it

You have to declare what kind of variable it is

Can combine declaration and assignment

Can declare multiple variables on one line

Concat:

• To combine strings, use plus operator
• But be careful with number/string types
• Example: 2 + 3 + " hello " + 7 + 2*3
• Multiplication first
• Then only addition is left, so evaluate left to right
• 2+3 first becomes 5
• Then the remaining plus operators turn into string concatenation operators
• Better: be explicit about what types are being added to what, and in what order.

Increment/decrement:

• Useful shorthand operators

Section 2.3: For Loop

2.3 Definitions

Definitions:

• Control structure

2.3 Material

Purpose:

• Replace redundant tasks

Syntax of for loops

• Initialize a loop variable, create a condition
• Body of for loop is executed if condition is true
• Tracing loops
• Curly braces are important

Some patterns:

• If we want to execute a loop N times, can use two patterns: i=0, or i=1
• Nested for loops
• Print vs println with nested for loops

Section 2.4: Managing Complexity

2.4 Definitions

Definitions:

• Scope
• Localizing variables
• Infinite loop
• Pseudocode
• Class constant

2.4 Material

Scope:

• Helps to manage complexity of variable space
• Curly braces represent scope
• Variable defined inside braces is not defined outside those braces

Examine examples, errors, why it crashes, and how it crashes

Tracing a for loop:

• Initialization
• Test
• Body
• Update
• End

Pseudocode:

• Part of communicating about code
• Simple examples to give them an idea
• More complex pattern-finding, indices (2(i-1)), etc...
• Constants (for drawing patterns, e.g., number of lines)
• Public static final type name = (...) <-- permanently, same value, accessible by static methods
• We are still thinking PROCEDURALLY

Section 2.5: Case Study: Hourglass Figure

2.5 Material

Detailed example of how to work out a pattern and translate it into modular code.

Single-line pattern, indexing and offset shifts

Entire code, refactoring into methods and modularization

Overall: tackling a complex problem by breaking it down into simpler parts, taking small steps toward end goal, managing complexity

Chapter 2 Summary

Deliverables:

• Primitive type expressions and literals
• Casting
• Assigning/changing variable values
• For loops, for loop patterns
• Scope
• Pseudocode
• Constants

Assessment Material

Dealing with primitive types in expressions, and order of operations, etc.

• How to interpret incrementing and other assignment operators
• For loops:
  • Know how to follow control
  • Syntax
  • Curly braces
• Scope
• Pseudo code to describe how to draw a pattern
• Constants
  • Syntax
  • Explaining the purpose (e.g., which of the following would be a good variable to program as public static final z)
• 99 bottles of root beer

Chapter 2 Code

Lecture Code

Confused Operator code

• shows same operator in two different contexts with two different behaviors

Density Calculations

• Re-implements density calculations, but with a class constant

For pattern

• Illustrates how to print a simple pattern using nested for loops

Print sequence

• Print numbers from the sequence 2^n

Worksheet Code

Square root

• Use Newton's Method to compute the value of square roots

Chapter 2 Homework

HW Summary

(Recommended) Self-check problems: #2, #4, #8, #10, #14, #22, #25, #28, #34

(Required) Exercises: #3, #9, #12, #22

(Required) Projects: (none)

HW Detailed

Self-check:

• 2, 4 - order of operations
• 8, 10 - getting 1st, 2nd, 3rd digit of a number using Java
• 14 - variables on both LHS and RHS
• 22 - Tracing for loop
• 25 - Blastoff!
• 28 - three nested loops to print pattern
• 34- turn figure into table of char counts for ! and / in figure

Exercises:

• 3 - Fibonacci numbers
• 9 - Nested for loops for 40 character lines, 4 different patterns
• 12 - Nested for loops to create 000111222333...
• 22 - Java program to produce dollar figure (V of $ on * bkg)

Chapter 2 Goodies

Profiles

Isaac Newton

• Brilliant mathematician and physicist, discovered the Law of Gravitation of spheres, Newton's Laws of Motion
• Physics: Newton's Three Laws (body in motion stays in motion until acted upon, F=ma, for every action equal opposite reaction)
• Physics: Newton's Law of Gravitation (two planets, multi-body problem)
• Mathematics: invented the calculus, and as if that weren't enough, created Newton's Method for finding roots of equations (still used on modern computers to calculate square roots), binomial expansions, infinite series
• Optics: discovered light was a particle, uncovered nature of color and its connection to wavelengths of photons, white being combination of all colors
• Lucasian Professor of Mathematics at Cambridge
• Retired from Cambridge, worked as the Warden of the Mint
• Mint: London was having a financial crisis because of counterfeit money, Newton applied his talents to making coins and bank notes that could not be counterfeited (hard problem! making something that's hard to make a copy of, on a really really big scale)
• Economics: Newton was the first to devise a comprehensive system for paper money in the British economy, starting in London; this helped to make Britain a financial power, and made London the world's financial center, which it still is to this day

Puzzle 2

Puzzles/Fall 2016/Puzzle 2 - Et tu, brute? (Caesar cipher cryptograms with spaces)