1. Week 4 - Wednesday
CS 121

2. Last time What did we talk about last time? if statements
else statements
Nested selection statements

3. Questions?

4. Project 1

5. if Review

6. if( condition ) statement; Anatomy of an if Any boolean expression
The if part
if( condition )
statement;
Any single executable statement

7. Two different outcomes
Anatomy of an if-else
if( condition )
statement1;
else
statement2;
Two different outcomes

8. An if with multiple statements
if( condition ) {
statement1;
statement2; …
statementn; }
A whole bunch of statements

9. Nested ifs if( condition1 ) { statement1; if( condition2 )… }

10. if Examples

11. DNA Assume that you have a variable called base of type char
Let base contain one of: 'A', 'C', 'G', 'T'
Write a series of if- and else-statements that will print out the chemical name of the base denoted by the corresponding character
A -> Adenine
C -> Cytosine
G -> Guanine
T -> Thymine

12. Printing DNA bases
if( base == 'A' )
System.out.println("Adenine");
else if( base == 'C' )
System.out.println("Cytosine");
else if( base == 'G' )
System.out.println("Guanine");
else if( base == 'T' )
System.out.println("Thymine");
else
System.out.println("Your base doesn't " + "belong to us");
What if you want to take care of upper and lower cases?

13. Upper and lower case bases using logic
if( base == 'A' || base == 'a' )
System.out.println("Adenine");
else if( base == 'C' || base == 'c' )
System.out.println("Cytosine");
else if( base == 'G' || base == 'g' )
System.out.println("Guanine");
else if( base == 'T' || base == 't' )
System.out.println("Thymine");
else
System.out.println("Your base doesn't " + "belong to us");
Is there a simpler way?

14. Upper and lower case bases using character conversion
base = Character.toUpperCase( base );
if( base == 'A' )
System.out.println("Adenine");
else if( base == 'C' )
System.out.println("Cytosine");
else if( base == 'G' )
System.out.println("Guanine");
else if( base == 'T' )
System.out.println("Thymine");
else
System.out.println("Your base doesn't " + "belong to us");

15. switch statements

16. if statements are okay…
But, didn't that DNA example seem a little clunky?
Surely, there is a cleaner way to express a list of possibilities
Enter: the switch statement

17. Anatomy of a switch statement
switch( data ) {
case value1:
statements 1;
case value2:
statements 2; …
case valuen:
statements n;
default:
default statements; }

18. DNA hittin' switches switch( base ) {
case 'A': System.out.println("Adenine");
break;
case 'C': System.out.println("Cytosine");
case 'G': System.out.println("Guanine");
case 'T': System.out.println("Thymine");
default: System.out.println("Your base" + "doesn't belong to us");
break; // unnecessary }
Go to SwitchMonth

19. Peculiarities of switch
Both "Three" and "Four" are printed
int data = 3;
switch( data ) {
case 3: System.out.println("Three");
case 4:
System.out.println("Four");
break;
case 5:
System.out.println("Five"); }
Go to SwitchAge
The break is optional
The default is optional too

20. Rules for switch
The data that you are performing your switch on must be an int, a char, or a String
The value for each case must be a literal
Execution will jump to the case that matches
If no case matches, it will go to default
If there is no default, it will skip the whole switch block
Execution will continue until it hits a break

21. DNA with upper and lower case
switch( base ) {
case 'A': case 'a':
System.out.println("Adenine");
break;
case 'C': case 'c':
System.out.println("Cytosine");
case 'G': case 'g':
System.out.println("Guanine");
case 'T': case 't':
System.out.println("Thymine");
default: System.out.println("Your base doesn't " + "belong to us");
break; // unnecessary }
Go to SwitchDays

22. A caution about switch Using if-statements is usually safer
if-statements are generally clearer and more flexible
switch statements are only for long lists of specific cases
Be careful about inconsistent use of break

23. Example 1
Write a program that reads in various ages and prints out any special abilities you gain at that age 16
Drive a car 17
Watch R-rated movies 18
Vote and smoke 21
Drink 25
Rent cars 30
Be a senator 35
Be president

24. Anniversary
Traditional
1st
Paper
2nd
Cotton
3rd
Leather
4th
Fruit or Flowers
5th
Wood
6th
Candy or Iron
7th
Wool or Copper
8th
Pottery or Bronze
9th
Willow or Pottery
10th
Tin or Aluminum
20th
China
25th
Silver
30th
Pearl
35th
Coral
40th
Ruby
45th
Sapphire
50th
Gold
60th
Diamond
Example 2
Write a program that reads in wedding anniversaries and gives the traditional gift for that anniversary

25. Example 3
Write a program that will read in a positive integer and print out the corresponding ordinal number
Number
Ordinal 1
1st 11
11th 2
2nd 12
12th 3
3rd 13
13th 4
4th 21
21st 5
5th 22
22nd 6
6th 23
23rd

26. Quiz

27. Upcoming

28. Next time…
Review
Lab 4

29. Reminders Keep reading Chapter 4 of the textbook
Keep working on Project 1
Due this Friday!
Exam 1 next Monday