1. Chapter 2
Programming Basics

2. Basic Data Concepts Primitive Data Types Expressions Literals
Arithmetic Operators
Precedence
Mixing Types and Casting

3. Data types type: A category or set of data values.
Constrains the operations that can be performed on data
Many languages ask the programmer to specify types
Examples: integer, real number, string
Internally, computers store everything as 1s and 0s
104 
"hi" 
ask them, how might the computer store "hi" using binary digits? (some kind of mapping; ASCII)

4. Java's primitive types
primitive types: 8 simple types for numbers, text, etc.
Java also has object types, which we'll talk about later
Name Description Examples
int integers (up to ) 42, -3, 0,
double real numbers (up to 10308) 3.1, , 9.4e3
char single text characters 'a', 'X', '?','\n'
boolean logical values true, false
The others: byte, float, long, and short
Why does Java distinguish integers vs. real numbers?
We're basically going to manipulate letters and numbers.
We make the integer / real number distinction in English as well. We don't ask, "How many do you weigh?" or, "How much sisters do you have?"
Part of the int/double split is related to how a computer processor crunches numbers. A CPU does integer computations and a Floating Point Unit (FPU) does real number computations.
Why does Java separate int and double? Why not use one combined type called number? 4

5. Expressions expression: A value or operation that computes a value.
Examples: * 5
(7 + 2) * 6 / 3 42
The simplest expression is a literal value.
-242
“Hello World”
3.4
A complex expression can use operators and parentheses.

6. Arithmetic operators
operator: Combines multiple values or expressions.
+ addition
- subtraction (or negation)
* multiplication
/ division
% modulus (a.k.a. remainder)
As a program runs, its expressions are evaluated.
1 + 1 evaluates to 2
System.out.println(3 * 4); prints 12
How would we print the text 3 * 4 ?

7. Integer division with /
When we divide integers, the quotient is also an integer.
14 / 4 is 3, not 3.5
4 ) ) ) 1425 54 21
More examples:
32 / 5 is 6
84 / 10 is 8
156 / 100 is 1
Dividing by 0 causes an error when your program runs.

8. Integer remainder with %
The % operator computes the remainder from integer division.
14 % 4 is 2
218 % 5 is ) )
Applications of % operator:
Obtain last digit of a number: % 10 is 7
Obtain last 4 digits: % is 6489
See whether a number is odd: 7 % 2 is 1, 42 % 2 is 0
What is the result?
45 % 6
2 % 2
8 % 20
11 % 0
What is 8 % 20? It's 8, but students often say 0. 8

9. Precedence precedence: Order in which operators are evaluated.
Generally operators evaluate left-to-right is (1 - 2) - 3 which is -4
But * / % have a higher level of precedence than * 4 is 13
6 + 8 / 2 * 3
* 3
is 18
Parentheses can force a certain order of evaluation: (1 + 3) * 4 is 16
Spacing does not affect order of evaluation 1+3 * 4-2 is 11

10. Precedence examples 1 * 2 + 3 * 5 % 4 \_/ | 2 + 3 * 5 % 4
\_/ | * 5 % 4
\_/ | % 4
\___/ |
\________/ |
1 + 8 % 3 * 2 - 9
\_/ | * 2 - 9
\___/ |
\______/ |
\_________/ |
Ask the students what 15 / 4 and 2 / 3 are, since the answers are non-obvious.

11. Precedence questions – Partner up
What values result from the following expressions?
9 / 5
695 % 20
7 + 6 * 5
7 * 6 + 5
248 % 100 / 5
6 * / 4
(5 - 7) * 4
6 + (18 % ( ))
8 % 20
2 / 3 * 834
(I don't usually go through these in lecture; I tell them they are extra problems they can work on later)
Answers: 1 15 37 47 9 16 -8 11

12. Real numbers (type double)
Examples: , , e17
Placing .0 or . after an integer makes it a double.
The operators + - * / % () all still work with double.
/ produces an exact answer: / 2.0 is 7.5
Precedence is the same: () before * / % before + -
Point out that it's odd for 42.0 to be considered a real number, but it is. 12

13. Real number example 2.0 * 2.4 + 2.25 * 4.0 / 2.0
\___/ | * 4.0 / 2.0
\___/ | / 2.0
\_____/ |
\____________/ |

14. Mixing types When int and double are mixed, the result is a double.
The conversion is per-operator, affecting only its operands.
7 / 3 * / 2
\_/ | * / 2
\___/ | / 2
\_/ |
\________/ |
3 / 2 is 1 above, not 1.5.
/ 3 * / 4
\___/ | * / 4
\_____/ | / 4
\_/ |
\_________/ |
\______________/ |
I don't usually go through the expression on the right; I just show it very quickly and move on.

15. Casting “Casting a value in a different type” (int) 32.4
Results in 32
Casting an expression
Use parentheses to cast the expression evaluation and not just one of the operands.
(int) (2.5 / .15)
Results in 16
(int) 2.5 / .15
Results in 13.3

16. Review Data Concepts What are Primitive Data Types?
8 simple types for numbers, text, etc.
What is an Expression?
expression: A value or operation that computes a value.
What is an Literal?
The simplest expression is a literal value, which doesn’t involve operators.
Arithmetic Operators
Combines multiple values or expressions. (+ - / * %)
Precedence
Order in which operators are evaluated.
Mixing Types and Casting
When int and double are mixed, the result is a double.

17. Variables Assignment/Declaration Variations String Concatenation
Variables and Mixing Types 17

18. Receipt example What's bad about the following code?
// Calculate total owed, assuming 9.5% tax / 15% tip
public class Receipt {
public static void main(String[] args) {
System.out.println("Subtotal:");
System.out.println( );
System.out.println("Tax:");
System.out.println(( ) * .08);
System.out.println("Tip:");
System.out.println(( ) * .15);
System.out.println("Total:");
System.out.println(
( ) *
( ) * .15); }
The subtotal expression ( ) is repeated
So many println statements

19. Variables
variable: A piece of the computer's memory that is given a name and type, and can store a value.
Like preset stations on a car stereo, or smart phone speed dial:
Steps for using a variable:
Declare it - state its name and type
Initialize it - store a value into it
Use it - print it or use it as part of an expression
a variable is also like the MS / MR buttons on a calculator
variables must be declared before they are used, just like methods 19

20. Declaration
variable declaration: Sets aside memory for storing a value.
Variables must be declared before they can be used.
Syntax:
type name;
The name is an identifier.
int x;
double myGPA; x
myGPA

21. Assignment assignment: Stores a value into a variable. Syntax:
The value can be an expression; the variable stores its result.
Syntax:
name = expression;
int x; x = 3;
double myGPA; myGPA = ( )/ 2; x
myGPA
3.5

22. Using variables
Once given a value, a variable can be used in expressions:
int x;
x = 3;
System.out.println("x is " + x); // x is 3
System.out.println(5 * x - 1); // 5 * 3 - 1
You can assign a value more than once:
int x; x = 3; System.out.println(x + " here"); // 3 here x = 4 + 7; System.out.println("now x is " + x); // now x is 11 x 11 x 3

23. Declaration/initialization
A variable can be declared/initialized in one statement.
Syntax:
type name = value;
double myGPA = 3.95;
int x = (11 % 3) + 12;
myGPA
3.95 x 14

24. Assignment and algebra
Assignment uses = , but it is not an algebraic equation.
= means, "store the value at right in variable at left"
The right side expression is evaluated first, and then its result is stored in the variable at left.
What happens here?
int x = 3;
x = x + 2; // ???
x = x + 2; increases the value stored in variable x by two. x 3 x 5 24

25. Assignment and types
A variable can only store a value of its own type.
int x = 2.5; // ERROR: incompatible types
An int value can be stored in a double variable.
The value is converted into the equivalent real number.
double myGPA = 4;
double avg = 11 / 2;
Why does avg store 5.0 and not 5.5 ?
myGPA
4.0
avg
5.0

26. A Quick Advance Console Input
Input, despite being necessary for most useful programs, is pretty complicated
Java has numerous methods for getting input from a bunch of different sources
keyboard, local files, web pages, network resources, etc.
For now, we will focus on one simple method for reading input from the keyboard
Don’t worry about the details of how this works for now

27. A Quick Advance Console Input
Keyboard Input
//use existing java library
import java.util.Scanner;
//insert class name and main
//initialize string for keyboard input
String inputString = null;
System.out.print("Input Command: ");
Scanner console = new Scanner(System.in);
// Get input from the keyboard.
inputString = console.nextLine();
// Echo the input.
System.out.print(inputString);

28. Simon Exercise
Exercise: Write a program to ask the user their name and favorite number, and then greet them.
Hello, what’s your name?
Dave
What is your favorite number? 7
Nice to meet you, Dave!
Your favorite number is 7.
//use existing java library
import java.util.Scanner;
public class Simon {
public static void main(String[] args) {
//insert class name and main
//initialize string for keyboard input
String inputString = null;
System.out.print("Input Command: ");
Scanner console = new Scanner(System.in);
// Get input from the keyboard.
inputString = console.nextLine();
// Echo the input.
System.out.print(“The Command you typed was” + inputString);
console.close(); }

29. Mixing types When int and double are mixed, the result is a double.
The conversion is per-operator, affecting only its operands.
7 / 3 * / 2
\_/ | * / 2
\___/ | / 2
\_/ |
\________/ |
3 / 2 is 1 above, not 1.5.
/ 3 * 2.5 – 6. / 4
\___/ | * 2.5 – 6. / 4
\_____/ | / 4
\_/ |
\_________/ |
\______________/ |
I don't usually go through the expression on the right; I just show it very quickly and move on.

30. Compiler errors A variable can't be used until it is assigned a value.
int x;
System.out.println(x); // ERROR: x has no value
You may not declare the same variable twice.
int x; int x; // ERROR: x already exists
int x = 3; int x = 5; // ERROR: x already exists
How can this code be fixed?

31. String concatenation
string concatenation: Using + between a string and another value to make a longer string.
"hello" + 42 is "hello42"
1 + "abc" + 2 is "1abc2"
"abc" is "abc12"
"abc" is "3abc"
"abc" + 9 * 3 is "abc27"
"1" + 1 is "11"
"abc" is "3abc"
Use + to print a string and an expression's value together.
System.out.println("Grade: " ( ) / 2);
Output: Grade: 83.5

32. Printing a variable's value
Use + to print a string and a variable's value on one line.
double grade = ( ) / 3.0;
System.out.println("Your grade was " + grade);
int students = ;
System.out.println("There are " + students +
" students in the course.");
Output:
Your grade was 83.2
There are 65 students in the course.

33. Review What is the result of this expression: "abc" + 1 + 2
How do you print to the console the value of a variable?
double grade = ( ) / 3.0;
System.out.println("Your grade was " + grade);

34. Receipt question Improve the receipt program using variables.
public class Receipt {
public static void main(String[] args) {
// Calculate total owed, assuming 9.5% tax / 15% tip
System.out.println("Subtotal:");
System.out.println( );
System.out.println("Tax:");
System.out.println(( ) * .08);
System.out.println("Tip:");
System.out.println(( ) * .15);
System.out.println("Total:");
System.out.println(
( ) * .15 +
( ) * .095); }

35. Receipt answer
public class Receipt { public static void main(String[] args) { // Calculate total owed, assuming 9.5% tax // 15% tip double subtotal = ; double tax = subtotal * .095; double tip = subtotal * .15; double total = subtotal + tax + tip; System.out.println("Subtotal: " + subtotal); System.out.println("Tax: " + tax); System.out.println("Tip: " + tip); System.out.println("Total: " + total); }

36. Shopping Cart Exercise
Modify your Greetings program to now be a Shopping Cart
Ask their name and for the price of 3 items.
Output the following:
Subtotal
Tax (9.5%)
Tip (15%)
Final Bill

37. Conditionals - if/else statements
Relational operators
Nested if/else statements
Object equality
Factoring if/else statements
Testing multiple conditions

38. Executes a block of statements only if a test is true
The if statement
Executes a block of statements only if a test is true
if (test) {
statement;
... }
Example:
double gpa = console.nextDouble();
if (gpa >= 2.0) {
System.out.println("Application accepted.");

39. Executes one block if a test is true, another if false
The if/else statement
Executes one block if a test is true, another if false
if (test) {
statement(s);
} else { }
Example:
double gpa = console.nextDouble();
if (gpa >= 2.0) {
System.out.println("Welcome to Mars University!");
System.out.println("Application denied.");

40. Relational expressions
if statements and for loops both use logical tests.
if (i <= 10) { ...
for (int i = 1; i <= 10; i++) { ...
These are boolean expressions, seen in Ch. 5.
Tests use relational operators:
Operator
Meaning
Example
Value ==
equals
1 + 1 == 2
true !=
does not equal
3.2 != 2.5
<
less than
10 < 5
false
>
greater than
10 > 5
<=
less than or equal to
126 <= 100
>=
greater than or equal to
5.0 >= 5.0
Note that == tests equality, not = . The = is used for the assignment operator!

41. Sample if/else – Using Relational Operators
public class MLBPlayoffs { public static void main(String[] args){ int mariners = 4; int angels = 1; int athletics = 4; int rangers = 0; if (mariners > angels) { if (rangers > athletics) { System.out.println("Mariners play game 163!"); } else{ System.out.println("Mariners won, but didn't make it to game 163"); else { System.out.println("Mariners lost.");

42. Misuse of if What's wrong with the following code?
Scanner console = new Scanner(System.in);
System.out.print("What percentage did you earn? ");
int percent = console.nextInt();
if (percent >= 90) {
System.out.println("You got an A!"); }
if (percent >= 80) {
System.out.println("You got a B!");
if (percent >= 70) {
System.out.println("You got a C!");
if (percent >= 60) {
System.out.println("You got a D!");
if (percent < 60) {
System.out.println("You got an F!");
...

43. Chooses between outcomes using many tests
Nested if/else
Chooses between outcomes using many tests
if (test) {
statement(s);
} else if (test) {
} else { }
Example:
if (x > 0) { //test1
System.out.println("Positive");//statement1
} else if (x < 0) {//test2
System.out.println("Negative");//statement2
System.out.println("Zero");//statement3

44. Nested if/else/if Example:
If it ends with else, exactly one path must be taken.
If it ends with if, the code might not execute any path.
if (test) {
statement(s);
} else if (test) { }
Example:
if (place == 1) {
System.out.println("Gold medal!");
} else if (place == 2) {
System.out.println("Silver medal!");
} else if (place == 3) {
System.out.println("Bronze medal.");

45. Nested if structures exactly 1 path (mutually exclusive)
if (test) {
statement(s);
} else if (test) {
} else { }
0 or 1 path (mutually exclusive)
0, 1, or many paths (independent tests; not exclusive)

46. Which nested if/else?
(1) if/if/if (2) nested if/else (3) nested if/else if
Whether a student is in elementary, middle, high school, or college.
(2) nested if / else if / else
Whether you made the dean's list (GPA ≥ 3.8) or honor roll ( ).
(3) nested if / else if
Whether a number is divisible by 2, 3, and/or 5.
(1) sequential if / if / if
Computing a grade of A, B, C, D, or F based on a percentage.
(2) nested if / else if / else if / else if / else

47. Exercise Formula for body mass index (BMI):
Weight class
below 18.5
underweight
normal
overweight
30.0 and up
obese
Formula for body mass index (BMI):
Write a program that produces output like the following:
This program reads data for two people and
computes their body mass index (BMI).
Enter next person's information:
height (in inches)? 70.0
weight (in pounds)?
height (in inches)? 62.5
weight (in pounds)? 130.5
Person 1 BMI =
overweight
Person 2 BMI =
normal
Difference =
// This program computes two people's body mass index (BMI) and
// compares them. The code uses parameters, returns, and Scanner.
import java.util.*; // so that I can use Scanner
public class BMI {
public static void main(String[] args) {
System.out.println("This program reads in data for two people and");
System.out.println("computes their body mass index (BMI)");
System.out.println();
// finish me! }

48. Nested if/else answer
// This program computes a person's body mass index (BMI).
import java.util.*;
public class BMI {
public static void main(String[] args) {
double height;
double weight;
double bodyMass;
// prints a welcome message explaining the program
System.out.println("This program reads data for a person and");
System.out.println("computes their body mass index (BMI).");
System.out.println();
// Ask the user for their height and weight.
Scanner console = new Scanner(System.in);
System.out.println("Enter the person's information:");
System.out.print("height (in inches)? ");
height = console.nextDouble();
System.out.print("weight (in pounds)? ");
weight = console.nextDouble();
...

49. Nested if/else, cont'd. // Compute the user's BMI.
bodyMass = weight * 703 / (height * height);
System.out.println("BMI = " + bodyMass);
// Determine the user's weight status.
if (bodyMass < 18.5) {
System.out.println("underweight");
} else if (bodyMass < 25) {
System.out.println("normal");
} else if (bodyMass < 30) {
System.out.println("overweight");
} else {
System.out.println("obese"); }
How would we round the BMI numbers?

50. Review What is a conditional statement in Java?
If/else
Example: If (test){ }
What is a Nested If statement?
if (test){
System.out.println(“Inside first test”);
else if (test2){ or
If (test){
If (test2 ){
System.out.println(“Inside second test”);
What kind of operator is ==?
Relational
What is it used for?
Test equality of the two operands

51. Equality operator for objects
The == operator does not work for objects, such as Strings
// Not Valid
String name = "Test";
if (name == "Dave"){}
Instead use the equals or equalsIgnoreCase methods
// Valid
if (name.equals("Dave")){}
// Also valid. As name implies case is ignored.
if (name.equalsIgnoreCase("Dave")){}

52. Logical operators Tests can be combined using logical operators:
"Truth tables" for each, used with logical values p and q:
Operator
Description
Example
Result
&&
and
(2 == 3) && (-1 < 5)
false || or
(2 == 3) || (-1 < 5)
true !
not
!(2 == 3) p q
p && q
p || q
true
false p !p
true
false

53. Evaluating logic expressions
Relational operators have lower precedence than math.
5 * 7 >= * (7 - 1)
5 * 7 >= * 6
35 >=
35 >= 33
true
Relational operators cannot be "chained" as in algebra.
2 <= x <= 10
true <= (assume that x is 15)
error!
Instead, combine multiple tests with && or ||
2 <= x && x <= 10
true && false
false

54. Logical questions
What is the result of each of the following expressions?
int x = 42;
int y = 17;
int z = 25;
y < x && y <= z
x % 2 == y % 2 || x % 2 == z % 2
x <= y + z && x >= y + z
!(x < y && x < z)
(x + y) % 2 == 0 || !((z - y) % 2 == 0)
Answers: true, false, true, true, false

55. Sample if/else – Using Logical Operators
public class MLBPlayoffs {
public static void main(String[] args){
int mariners = 4;
int angels = 1;
int athletics = 4;
int rangers = 0;
if ((mariners > angels) && (rangers > athletics)){
System.out.println("Mariners play game 163!"); }
else if (mariners > angels){
System.out.println("Mariners won, but didn't make it to game 163.");
else {
System.out.println("Mariners lost.");

56. Shopping Cart Exercise Cont’d
Modify your Shopping Cart program to now be a Restaurant Shopping Cart that handles different tax and tip based upon the locale.
Ask their name, locale, and the price of 3 items.
Output the following:
Subtotal
Tax (taxRate)
Tip (tipRate)
Final Bill
Locale
Tax
Tip
Issaquah
9.5%
15%
Portland 0%
Los Angeles
9.0%
Paris
19.6%
Taipei
5.0%

57. The for loop
Tracing for loops
For loop patterns
Nested for loops 58

58. Repetition with for loops
So far, repeating a statement is redundant:
System.out.println("Homer says:");
System.out.println("I am so smart");
System.out.println("S-M-R-T... I mean S-M-A-R-T");
Java's for loop statement performs a task many times.
for (int i = 1; i <= 4; i++) { // repeat 4 times }
also related to book exercise 1.10 about printing 1000 copies of "All work and no play makes Jack a dull boy"

59. for loop syntax header for (initialization; test; update) { statement;
body
header
for (initialization; test; update) {
statement;
... }
Perform initialization once.
Repeat the following:
Check if the test is true. If not, stop.
Execute the statements.
Perform the update.

60. Initialization Tells Java what variable to use in the loop
for (int i = 1; i <= 6; i++) {
System.out.println("I am so smart"); }
Tells Java what variable to use in the loop
Performed once as the loop begins
The variable is called a loop counter
can use any name, not just i
can start at any value, not just 1

61. Test Tests the loop counter variable against a limit
for (int i = 1; i <= 6; i++) {
System.out.println("I am so smart"); }
Tests the loop counter variable against a limit
Uses relational operators:
< less than
<= less than or equal to
> greater than
>= greater than or equal to

62. Increment and decrement
shortcuts to increase or decrease a variable's value by 1
Shorthand Equivalent longer version
variable++; variable = variable + 1;
variable--; variable = variable - 1;
int x = 2;
x++; // x = x + 1;
// x now stores 3
double gpa = 2.5;
gpa--; // gpa = gpa - 1;
// gpa now stores 1.5

63. Loop walkthrough Output: 1 squared = 1 2 squared = 4 3 squared = 9
for (int i = 1; i <= 4; i++) {
System.out.println(i + " squared = " + (i * i)); }
System.out.println("Whoo!");
Output:
1 squared = 1
2 squared = 4
3 squared = 9
4 squared = 16
Whoo! 3 5 1 2 3 4 5

64. shortcuts to modify a variable's value
Modify-and-assign
shortcuts to modify a variable's value
Shorthand Equivalent longer version
variable += value; variable = variable + value;
variable -= value; variable = variable - value;
variable *= value; variable = variable * value;
variable /= value; variable = variable / value;
variable %= value; variable = variable % value;
x += 3; // x = x + 3;
gpa -= 0.5; // gpa = gpa - 0.5;
number *= 2; // number = number * 2;

65. Repetition over a range
System.out.println("1 squared = " + 1 * 1);
System.out.println("2 squared = " + 2 * 2);
System.out.println("3 squared = " + 3 * 3);
System.out.println("4 squared = " + 4 * 4);
System.out.println("5 squared = " + 5 * 5);
System.out.println("6 squared = " + 6 * 6);
Intuition: "I want to print a line for each number from 1 to 6"
The for loop does exactly that!
for (int i = 1; i <= 6; i++) {
System.out.println(i + " squared = " + (i * i)); }
"For each integer i from 1 through 6, print ..."

66. Multi-line loop body System.out.println("+----+");
for (int i = 1; i <= 3; i++) {
System.out.println("\\ /");
System.out.println("/ \\"); }
Output:
+----+
\ /
/ \

67. Review What does this operator do: ++
Increment a variable
How do you repeat a set of statements a fixed number of times in Java?
Use the for loop

68. Even numbers Exercise Print out the even numbers from 1 – 200
Use for and if statements
Remember the % operator
If you finish early
Write a program that asks a user for number and then returns the sum of the cubes from 1 to the number
…. + N3

69. Counting down The update can use -- to make the loop count down.
The test must say > instead of <
System.out.print("T-minus ");
for (int i = 10; i >= 1; i--) {
System.out.print(i + ", "); }
System.out.println("blastoff!");
System.out.println("The end.");
Output:
T-minus 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, blastoff!
The end.

70. Nested for loops

71. Nested loops nested loop: A loop placed inside another loop. Output:
for (int i = 1; i <= 5; i++) {
for (int j = 1; j <= 10; j++) {
System.out.print("*"); }
System.out.println(); // to end the line
Output:
**********
The outer loop repeats 5 times; the inner one 10 times.
"sets and reps" exercise analogy
How would we print a multiplication table?
try printing each of the following inside the inner loop:
System.out.print(i + " ");
System.out.print(j + " ");
System.out.print((i * j) + " ");

72. Expressions for loop counter
int highTemp = 11;
for (int i = 0; i <= highTemp / 2; i++) {
// outputs temperatures in fahrenheit
System.out.println(i * ); }
Output:
32.0
33.8
35.6
37.4
39.2
41.0

73. Nested for loop exercise
// Outer loop.
for (int i = 1; i <= 5; i++) {
// Inner loop.
for (int j = 1; j <= i; j++) {
System.out.print("*"); }
System.out.println();
Output: * **
***
****
*****

74. Nested for loop exercise
What is the output of the following nested for loops?
// outer loop
for (int i = 1; i <= 5; i++) {
//inner loop
for (int j = 1; j <= i; j++) {
System.out.print(i); }
System.out.println();
Output: 1 22
333
4444
55555

75. Common errors
Both of the following sets of code produce infinite loops:
for (int i = 1; i <= 5; i++) {
for (int j = 1; i <= 10; j++) {
System.out.print("*"); }
System.out.println();
for (int j = 1; j <= 10; i++) {
Both cases produce infinite loops. 76

76. Complex lines What nested for loops produce the following output?
....1
...2
..3 .4 5
We must build multiple complex lines of output using:
an outer "vertical" loop for each of the lines
inner "horizontal" loop(s) for the patterns within each line
outer loop (loops 5 times because there are 5 lines)
inner loop (repeated characters on each line)

77. Outer and inner loop
First write the outer loop, from 1 to the number of lines.
for (int line = 1; line <= 5; line++) {
... }
Now look at the line contents. Each line has a pattern:
some dots (0 dots on the last line), then a number
....1
...2
..3 .4 5
Observation: the number of dots is related to the line number.
5 – line

78. Mapping loops to numbers
for (int count = 1; count <= 5; count++) {
System.out.print( ... ); }
What statement in the body would cause the loop to print:
System.out.print(3 * count " ");

79. Loop tables What statement in the body would cause the loop to print:
To see patterns, make a table of count and the numbers.
Each time count goes up by 1, the number should go up by 5.
But count * 5 is too great by 3, so we subtract 3.
count
number to print 1 2 7 3 12 4 17 5 22
5 * count 5 10 15 20 25
5 * count - 3 2 7 12 17 22

80. Loop tables question
What statement in the body would cause the loop to print:
Let's create the loop table together.
Each time count goes up 1, the number printed should ...
But this multiple is off by a margin of ...
count
number to print 1 17 2 13 3 9 4 5
-4 * count -4 -8
-12
-16
-20
-4 * count
-4 * count + 21 -4 17 -8 13
-12 9
-16 5
-20 1

81. Nested for loop exercise – Partner up
Make a table to represent any patterns on each line.
....1
...2
..3 .4 5
To print a character multiple times, use a for loop.
for (int j = 1; j <= 4; j++) {
System.out.print("."); // 4 dots }
line
# of dots 1 4 2 3 5
-1 * line -1 -2 -3 -4 -5
-1 * line + 5 4 3 2 1

82. Nested for loop solution
Answer:
for (int line = 1; line <= 5; line++) {
for (int j = 1; j <= (-1 * line + 5); j++){
System.out.print("."); }
System.out.println(line);
Output:
....1
...2
..3 .4 5

83. Nested for loop exercise
What is the output of the following nested for loops?
for (int line = 1; line <= 5; line++) {
for (int j = 1; j <= (-1 * line + 5); j++) {
System.out.print("."); }
for (int k = 1; k <= line; k++) {
System.out.print(line);
System.out.println();
Answer:
....1
...22
..333
.4444
55555

84. Exercises
Modify your EvenNumbers program to output the even numbers from to output a table with 10 numbers per line using nested for loops. ….
Rotating Single Digits
Output a rotating, increasing list of single-digit numbers. Each line is 50 characters wide
| | | | |
Dots and numbers
Output the following:
....1
...2.
..3..
.4...
5....

85. Nested for loop exercise
Modify the previous code to produce this output:
....1
...2.
..3..
.4...
5....
Answer:
for (int line = 1; line <= 5; line++) {
for (int j = 1; j <= (-1 * line + 5); j++) {
System.out.print("."); }
System.out.print(line);
for (int j = 1; j <= (line - 1); j++) {
System.out.println();
If you have time left over at this point (you probably won't), you could ask them how to make the loop print 12 lines instead of 5. (leads in to constants in next lecture)

86. Developing algorithms

87. Where are we going?
Write a program that uses nested for loops to create the following hourglass.
|””””””””””| Quotes=10
\::::::::/
\::::::/
\::::/
\::/ ||
/::\
/::::\
/::::::\
/::::::::\
|””””””””””|
Top Half
Row
Spaces
Colons 1 8 2 6 3 4

88. Development strategy
Task: Use nested for loops to produce the following output.
Recommendations for managing complexity:
Design the algorithm using Pseudo-code.
write an English description of steps required
use this description to decide the methods
If needed, create a table of patterns of characters
Use table to write your for loops
Write your code/methods.
#================#
| <><> |
| <>....<> |
| <> <> |
|<> <>|

89. Aside: Why draw ASCII art?
ASCII art has complex patterns
Can focus on the algorithms
#================#
| <><> |
| <>....<> |
| <> <> |
|<> <>|

90. 1. Pseudo-code pseudo-code: An English description of an algorithm.
Example: Drawing a 12 wide by 7 tall box of stars
print 12 stars.
for (each of 5 lines) {
print a star.
print 10 spaces. }
************
* *

91. Pseudo-code algorithm
Take 1 minute to discuss with your partner the patterns you see in the graphic below
1. Line
# , 16 =, #
2. Top half |
spaces (decreasing)
<>
dots (increasing)
spaces (same as above)
3. Bottom half
(top half upside-down)
4. Line
#================#
| <><> |
| <>....<> |
| <> <> |
|<> <>|

92. Pseudo-code public class Mirror {
public static void main(String[] args) {
//line
line();
// top half
topHalf();
// bottom half
bottomHalf();
// line }

93. Pseudo-code with methods
public class Mirror {
public static void main(String[] args) {
//line
line();
// top half
topHalf();
// bottom half
bottomHalf();
// line }
public static void line(){
// # , 16 =, #
public static void topHalf(){
// |
// spaces (decreasing)
// <>
// dots (increasing)
// spaces (same as above)
public static void bottomHalf(){
// (top half upside-down)

94. Pseudo-code with for loops
public class Mirror { public static void main(String[] args) { //line line(); // top half topHalf(); // bottom half bottomHalf(); // line } public static void line(){ // # , 16 =, # public static void topHalf(){ for (int line = 1; line <= 4; line++){ // | // spaces (decreasing) // <> // dots (increasing) // spaces (same as above) public static void bottomHalf(){ // (top half upside-down)

95. 2. Tables A table for the top half:
Compute spaces and dots expressions from line number
Why do we want to create an expression in terms of the line number?
line
spaces
line *
dots
4 * line - 4 1 6 2 4 3 8 12
line
spaces
dots 1 6 2 4 3 8 12
#================#
| <><> |
| <>....<> |
| <> <> |
|<> <>|

96. 2. Tables cont’d A table for the bottom half:
Compute spaces and dots expressions from line number
line
spaces
line * 2 - 2
dots
line * 1 6 12 2 4 8 3
line
spaces
dots 1 12 2 8 3 4 6
#================#
| <><> |
| <>....<> |
| <> <> |
|<> <>|

97. 3. Writing the code Useful questions about the top half:
What methods? (think structure and redundancy)
Number of (nested) loops per line?
#================#
| <><> |
| <>....<> |
| <> <> |
|<> <>|

98. Partial solution
// Prints the expanding pattern of <> // for the top half of the figure. public static void topHalf(){ for (int line = 1; line <= 4; line++){ // | System.out.print("|"); // spaces (decreasing) for (int spaces = 1; spaces <= line * ; spaces++){ System.out.print(" "); } // <> System.out.print("<>"); // dots (increasing) for (int dots = 1; dots <= 4 * line - 4;dots++){ System.out.print("."); // spaces (same as above) System.out.println("|");

99. Development strategy Review
What is the 1st step that I want you to do in developing your algorithm?
Design the algorithm using Pseudo-code.
If needed, create a table of patterns of characters
Use table to write your for loops
Write your code/methods.

100. Hourglass Exercise
Write a program that uses nested for loops to create the following hourglass.
|””””””””””| Quotes=10
\::::::::/
\::::::/
\::::/
\::/ ||
/::\
/::::\
/::::::\
/::::::::\
|””””””””””|
Top Half
Row
Spaces
Colons 1 8 2 6 3 4

101. Hourglass Exercise
Write a program that uses nested for loops to create the following hourglass.
|””””””””””| Quotes=10
\::::::::/
\::::::/
\::::/
\::/ ||
/::\
/::::\
/::::::\
/::::::::\
|””””””””””|
Top Half
Row
Spaces
Colons 1 8 2 6 3 4

102. Class constants and scope
103

103. Scaling the mirror
Let's modify our Mirror program so that it can scale.
The current mirror (left) is at size 4; the right is at size 3.
The number of rows in the top or bottom
We'd like to structure the code so we can scale the figure by changing the code in just one place.
#================#
| <><> |
| <>....<> |
| <> <> |
|<> <>|
#============#
| <><> |
| <>....<> |
|<> <>|

104. Limitations of variables
Idea: Make a variable to represent the size.
Use the variable's value in the methods.
Problem: A variable in one method can't be seen in others.
public static void main(String[] args) {
int size = 4;
topHalf();
printBottom(); }
public static void topHalf() {
for (int i = 1; i <= size; i++) { // ERROR: size not found
...
public static void bottomHalf() {
for (int i = size; i >= 1; i--) { // ERROR: size not found
105

105. Scope
scope: The part of a program where a variable exists.
From its declaration to the end of the { } braces
A variable declared in a for loop exists only in that loop.
A variable declared in a method exists only in that method.
public static void example() {
int x = 3;
for (int i = 1; i <= 10; i++) {
System.out.println(x); }
// i no longer exists here
} // x ceases to exist here
x's scope
i's scope

106. Scope implications
Variables without overlapping scope can have same name.
for (int i = 1; i <= 100; i++) {
System.out.print("/"); }
for (int i = 1; i <= 100; i++) { // OK
System.out.print("\\");
int i = 5; // OK: outside of loop's scope
A variable can't be declared twice or used out of its scope.
for (int i = 1; i <= 100 * line; i++) {
int i = 2; // ERROR: overlapping scope
i = 4; // ERROR: outside scope

107. Class constants
class constant: A fixed value visible to the whole program.
value can be set only at declaration; cannot be reassigned
Syntax:
public static final type name = value;
name is usually in ALL_UPPER_CASE
Examples:
public static final int DAYS_IN_WEEK = 7;
public static final double INTEREST_RATE = 3.5;
public static final int SSN = ;

108. Constants and figures
Consider the task of drawing the following scalable figure:
+/\/\/\/\/\/\/\/\/\/\+
| |
| | Multiples of 5 occur many times
| | For every vertical Pipe (|)
| | there are 2 /\
+/\/\/\/\+
| |
| | The same figure at size 2
109

109. Repetitive figure code
public class Sign { public static void main(String[] args) { drawLine(); drawBody(); } public static void drawLine() { System.out.print("+"); for (int i = 1; i <= 10; i++) { System.out.print("/\\"); System.out.println("+"); public static void drawBody() { for (int line = 1; line <= 5; line++) { System.out.print("|"); for (int spaces = 1; spaces <= 20; spaces++) { System.out.print(" "); System.out.println("|");
110

110. Adding a constant
public class Sign { public static final int HEIGHT = 5; public static void main(String[] args) { drawLine(); drawBody(); } public static void drawLine() { System.out.print("+"); for (int i = 1; i <= HEIGHT * 2; i++) { System.out.print("/\\"); System.out.println("+"); public static void drawBody() { for (int line = 1; line <= HEIGHT; line++) { System.out.print("|"); for (int spaces = 1; spaces <= HEIGHT * 4; spaces++) { System.out.print(" "); System.out.println("|");
111

111. Complex figure w/ constant
Modify the Mirror code to be resizable using a constant.
A mirror of size 4:
#================#
| <><> |
| <>....<> |
| <> <> |
|<> <>|
A mirror of size 3:
#============#
| <><> |
| <>....<> |
|<> <>|

112. Using a constant Constant allows many methods to refer to same value:
public static final int SIZE = 4;
public static void main(String[] args) {
topHalf();
printBottom(); }
public static void topHalf() {
for (int i = 1; i <= SIZE; i++) { // OK
...
public static void bottomHalf() {
for (int i = SIZE; i >= 1; i--) { // OK
113

113. Loop tables and constant
Let's modify our loop table to use SIZE
This can change the amount added in the loop expression
#================# #============#
| <><> | | <><> |
| <>....<> | | <>....<> |
| <> <> | |<> <>|
|<> <>| |<> <>|
|<> <>| | <>....<> |
| <> <> | | <><> |
| <>....<> | #============#
| <><> |
#================#
SIZE
line
spaces
dots 4
1,2,3,4
6,4,2,0
-2*line + 8
0,4,8,12
4*line - 4 3
1,2,3
4,2,0
-2*line + 6
0,4,8
SIZE
line
spaces
-2*line + (2*SIZE)
dots
4*line - 4 4
1,2,3,4
6,4,2,0
-2*line + 8
0,4,8,12 3
1,2,3
4,2,0
-2*line + 6
0,4,8
SIZE
line
spaces
dots 4
1,2,3,4
6,4,2,0
0,4,8,12 3
1,2,3
4,2,0
0,4,8

114. Partial solution
public static final int SIZE = 4; // Prints the expanding pattern of <> for the top half of the figure. public static void topHalf() { for (int line = 1; line <= SIZE; line++) { System.out.print("|"); for (int space = 1; space <= (line * -2 + (2*SIZE)); space++) { System.out.print(" "); } System.out.print("<>"); for (int dot = 1; dot <= (line * 4 - 4); dot++) { System.out.print("."); System.out.println("|");

115. Hourglass with Constants Exercise
Modify your Hourglass program that uses nested for loops to create the following hourglass. Use a constant to scale the hourglass
|””””””””””| SIZE=4;Quotes=10
\::::::::/
\::::::/
\::::/
\::/ ||
/::\
/::::\
/::::::\
/::::::::\
|””””””””””|
Top Half
Row
Spaces
Colons 1 8 2 6 3 4

116. Review Variables if statement Relational expressions and operators
Java’s primitive types
Expressions and String Concatenation
Expressions
Arithmetic operators
Precedence
Mixing types
String concatenation
if statement
Nested if/else if/else
Relational expressions and operators
Logical operators
for loop
nested for loop
Class constants and Scope

117. Variables
variable: A piece of the computer's memory that is given a name and type, and can store a value.
Like preset stations on a car stereo, or cell phone speed dial:
Steps for using a variable:
Declare it - state its name and type
Initialize it - store a value into it
Use it - print it or use it as part of an expression
a variable is also like the MS / MR buttons on a calculator
variables must be declared before they are used, just like methods
118

118. Java's primitive types
primitive types: 8 simple types for numbers, text, etc.
Java also has object types, which we'll talk about later
Name Description Examples
int integers (up to ) 42, -3, 0,
double real numbers (up to 10308) 3.1, , 9.4e3
char single text characters 'a', 'X', '?', '\n'
boolean logical values true, false
Why does Java distinguish integers vs. real numbers?
We're basically going to manipulate letters and numbers.
We make the integer / real number distinction in English as well. We don't ask, "How many do you weigh?" or, "How much sisters do you have?"
Part of the int/double split is related to how a computer processor crunches numbers. A CPU does integer computations and a Floating Point Unit (FPU) does real number computations.
Why does Java separate int and double? Why not use one combined type called number?
119

119. Expressions expression: A value or operation that computes a value.
Examples: * 5
(7 + 2) * 6 / 3 42
The simplest expression is a literal value.
-242
“Hello World”
3.4
A complex expression can use operators and parentheses.

120. Arithmetic operators
operator: Combines multiple values or expressions.
+ addition
- subtraction (or negation)
* multiplication
/ division
% modulus (a.k.a. remainder)
As a program runs, its expressions are evaluated.
1 + 1 evaluates to 2
System.out.println(3 * 4); prints 12
How would we print the text 3 * 4 ?

121. Precedence precedence: Order in which operators are evaluated.
Generally operators evaluate left-to-right is (1 - 2) - 3 which is -4
But * / % have a higher level of precedence than * 4 is 13
6 + 8 / 2 * 3
* 3
is 18
Parentheses can force a certain order of evaluation: (1 + 3) * 4 is 16
Spacing does not affect order of evaluation 1+3 * 4-2 is 11

122. Mixing types When int and double are mixed, the result is a double.
The conversion is per-operator, affecting only its operands.
7 / 3 * / 2
\_/ | * / 2
\___/ | / 2
\_/ |
\________/ |
3 / 2 is 1 above, not 1.5.
/ 3 * / 6
\___/ | * / 6
\_____/ | / 6
\_/ |
\_________/ |
\______________/ |
I don't usually go through the expression on the right; I just show it very quickly and move on.

123. String concatenation
string concatenation: Using + between a string and another value to make a longer string.
"hello" + 42 is "hello42"
1 + "abc" + 2 is "1abc2"
"abc" is "abc12"
"abc" is "3abc"
"abc" + 9 * 3 is "abc27"
"1" + 1 is "11"
"abc" is "3abc"
Use + to print a string and an expression's value together.
System.out.println("Grade: " ( ) / 2);
Output: Grade: 83.5

124. Executes a block of statements only if a test is true
The if statement
Executes a block of statements only if a test is true
if (test) {
statement;
... }
Example:
double gpa = console.nextDouble();
if (gpa >= 3.0) {
System.out.println("Application accepted.");

125. Chooses between outcomes using many tests
Nested if/else
Chooses between outcomes using many tests
if (test) {
statement(s);
} else if (test) {
} else { }
Example:
if (x > 0) {
System.out.println("Positive");
} else if (x < 0) {
System.out.println("Negative");
System.out.println("Zero");

126. Relational expressions
if statements and for loops both use logical tests.
if (i <= 10) { ...
for (int i = 1; i <= 10; i++) { ...
These are boolean expressions, seen in Ch. 5.
Tests use relational operators:
Operator
Meaning
Example
Value ==
equals
1 + 1 == 2
true !=
does not equal
3.2 != 2.5
<
less than
10 < 5
false
>
greater than
10 > 5
<=
less than or equal to
126 <= 100
>=
greater than or equal to
5.0 >= 5.0
Note that == tests equality, not = . The = is used for the assignment operator!

127. Logical operators Tests can be combined using logical operators:
"Truth tables" for each, used with logical values p and q:
Operator
Description
Example
Result
&&
and
(2 == 3) && (-1 < 5)
false || or
(2 == 3) || (-1 < 5)
true !
not
!(2 == 3) p q
p && q
p || q
true
false p !p
true
false

128. for loop syntax header for (initialization; test; update) { statement;
body
header
for (initialization; test; update) {
statement;
... }
Perform initialization once.
Repeat the following:
Check if the test is true. If not, stop.
Execute the statements.
Perform the update.

129. Class constants
class constant: A fixed value visible to the whole program.
value can be set only at declaration; cannot be reassigned
Syntax:
public static final type name = value;
name is usually in ALL_UPPER_CASE
Examples:
public static final int DAYS_IN_WEEK = 7;
public static final double INTEREST_RATE = 3.5;
public static final int SSN = ;

130. Scope
scope: The part of a program where a variable exists.
From its declaration to the end of the { } braces
A variable declared in a for loop exists only in that loop.
A variable declared in a method exists only in that method.
public static void example() {
int x = 3;
for (int i = 1; i <= 10; i++) {
System.out.println(x); }
// i no longer exists here
} // x ceases to exist here
x's scope
i's scope