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CS 121 Week 4 - Wednesday

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Page 1: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

CS 121Week 4 - Wednesday

Page 2: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Last time

What did we talk about last time?if statementselse statements Nested selection statements

Page 3: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Questions?

Page 4: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Project 1

Page 5: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

if Review

Page 6: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

The if part

Any boolean expression

Any single executable statement

Anatomy of an if

if( condition ) statement;

Page 7: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Anatomy of an if-else

Two different

outcomes

if( condition ) statement1;

elsestatement2;

Page 8: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

An if with multiple statements

if( condition ){

statement1;statement2;…statementn;

}

A whole bunch of

statements

Page 9: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Nested ifs

if( condition1 ){

statement1;if( condition2 ) {

if( condition3 )statement2;

…}

}

Page 10: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

if Examples

Page 11: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Speed limit answer

The simplest answer:

What if we want to add a message if the speed is legal?

if( speed > 3.0e8 )System.out.println("Not so fast!");

if( speed > 3.0e8 )System.out.println("Not so fast!");

elseSystem.out.println("That speed's fine.");

Page 12: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

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

Page 13: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Printing DNA bases

What if you want to take care of upper and lower cases?

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");

elseSystem.out.println("Your base doesn't " + "belong to us");

Page 14: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Upper and lower case bases using logic

Is there a simpler way?

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");

elseSystem.out.println("Your base doesn't " + "belong to us");

Page 15: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

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");

elseSystem.out.println("Your base doesn't " + "belong to us");

Page 16: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

switch statements

Page 17: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

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

Page 18: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Anatomy of a switch statement

switch( data ){

case value1:statements 1;

case value2:statements 2;

…case valuen:

statements n;default:

default statements;}

Page 19: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

DNA hittin' switches

switch( base ){case 'A': System.out.println("Adenine");

break;case 'C': System.out.println("Cytosine");

break;case 'G': System.out.println("Guanine");

break;case 'T': System.out.println("Thymine");

break;default: System.out.println("Your base" + "doesn't belong to us");

break; // unnecessary}

Page 20: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Peculiarities of switch

int data = 3;switch( data ){

case 3:System.out.println("Three");

case 4:System.out.println("Four");break;

case 5:System.out.println("Five");

}

Both "Three" and "Four" are

printed

The break is optional

The default is

optional too

Page 21: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Rules for switch

1. The data that you are performing your switch on must be an int, a char, or a String

2. The value for each case must be a literal3. Execution will jump to the case that

matches4. If no case matches, it will go to default5. If there is no default, it will skip the whole

switch block6. Execution will continue until it hits a break

Page 22: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

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");break;

case 'G': case 'g':System.out.println("Guanine");break;

case 'T': case 't':System.out.println("Thymine");break;

default: System.out.println("Your base doesn't " + "belong to us");

break; // unnecessary}

Page 23: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

A caution about switch

Using if-statements is usually saferif-statements are generally clearer

and more flexibleswitch statements are only for long

lists of specific cases Be careful about inconsistent use of break

Page 24: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

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

Page 25: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Example 2

Write a program that reads in wedding anniversaries and gives the traditional gift for that anniversary

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

Page 26: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Example 3

Write a program that will read in a positive integer and print out the corresponding ordinal number

Number Ordinal 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

Page 27: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Quiz

Page 28: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Upcoming

Page 29: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Next time…

Review Lab 4

Page 30: Week 4 - Wednesday. What did we talk about last time? if statements else statements Nested selection statements

Reminders

Keep reading Chapter 4 of the textbook

Keep working on Project 1 Due this Friday!

Exam 1 next Monday Office hours this Friday from 3:30-

5pm are canceled due to travel


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