1. COMP 14 Introduction to Programming
Michele Weigle - COMP 14 - Spring 2004
COMP 14 Introduction to Programming
Mr. Joshua Stough
February 9, 2005
Monday/Wednesday 11:00-12:15
Peabody Hall 218

2. Review Flow of Execution
Michele Weigle - COMP 14 - Spring 2004
Review Flow of Execution

3. Review Relational Operators
Michele Weigle - COMP 14 - Spring 2004
Review Relational Operators
Less than <
Greater than >
Equal to ==
not assignment ‘=‘
Not equal to !=
Less than or equal to <=
Greater than or equal to >=

4. Review Boolean Operators
Michele Weigle - COMP 14 - Spring 2004
Review Boolean Operators
NOT ! (unary)
!(2+2==5)
AND && (binary)
(2+2==5) && (1+1==2)
OR || (binary)
(2+2==5) || (1+1==2)
true
false
true

5. Michele Weigle - COMP 14 - Spring 2004
Selection
if statements
if-else statements
Nested if statements
switch statements
Textbook Reference: Chapter 4 (pgs )

6. Conditional Statements
Michele Weigle - COMP 14 - Spring 2004
Conditional Statements
Let us choose which statement will be executed next
also called selection statements
Java's conditional statements:
the if statement
the if-else statement
the switch statement
Conditional statement give us the power to make basic decisions about flow of control

7. Michele Weigle - COMP 14 - Spring 2004
One-Way Selection
Syntax: if (expression)
statement

8. Michele Weigle - COMP 14 - Spring 2004
The if Statement
The condition must be a boolean expression.
It must evaluate to either true or false.
if is a Java
reserved word
if ( condition )
statement;
If the condition is true, the statement is executed.
If it is false, the statement is skipped.

9. Michele Weigle - COMP 14 - Spring 2004
The if Statement
if (sum > MAX)
delta = sum - MAX;
System.out.println ("The sum is " + sum);
First, the condition is evaluated. The value of sum
is either greater than the value of MAX, or it is not.
If the condition is true, the assignment statement is
executed.
If it is not, the assignment statement is skipped.
Either way, the call to println is executed next.

10. Michele Weigle - COMP 14 - Spring 2004
Block Statements
Syntax: {
statement1
statement2 .
statementn }
We use curly braces to group a set of individual statements.
This way we can have multiple statements execute based on a decision.
If we don't use curly braces, only a single statement will be executed based on the result of a decision.

11. Michele Weigle - COMP 14 - Spring 2004
The if Statement
if (sum > MAX)
delta = sum - MAX;
System.out.println ("The sum is " + sum); A
if (sum > MAX) {
delta = sum - MAX; }
System.out.println ("The sum is " + sum); B
Code A and Code B do the exact same things. The braces point out a block of code.
A block is a group of one or more statements delimited by a set of curly braces. Anywhere we say a statement is executed, a block could have been executed
The braces in Code B allow us to add more than one statement that should execute if the condition is true. In these examples, Code C will execute only the println statement if the condition is true.
Notice the indentation of the code
remember that the computer ignores whitespace like tabs
Use braces even when not required
if (sum > MAX) {
delta = sum - MAX;
System.out.println ("The sum is " + sum); } C

12. Michele Weigle - COMP 14 - Spring 2004
Curly Braces
int num = 87, max = 25;
if (num >= max*2)
System.out.println ("apple");
System.out.println ("orange");
System.out.println ("pear");
int num = 87, max = 25;
if (num >= max*2) {
System.out.println ("apple"); }
System.out.println ("orange");
System.out.println ("pear");
These two code boxes produce the same output. Even though the indentation is incorrect, it's easier to tell what will be output when braces are used.

13. Michele Weigle - COMP 14 - Spring 2004
State.java Example

14. Michele Weigle - COMP 14 - Spring 2004
if Statement Gotcha
if (score >= 90);
grade = "A";
No matter the result of the condition,
grade will be assigned "A". The semicolon
after the if statement is a semantic error.

15. Michele Weigle - COMP 14 - Spring 2004
In-Class Exercises
What is printed by the following code fragment?
int num = 87, max = 25;
if (num >= max*2)
System.out.println ("apple");
System.out.println ("orange");
System.out.println ("pear");
apple
orange
pear
Write a code fragment that will print the value
of val if val is less than MAX.
if (val < MAX) {
System.out.println (val); }

16. Michele Weigle - COMP 14 - Spring 2004
Two-Way Selection

17. Michele Weigle - COMP 14 - Spring 2004
The if-else Statement
if ( condition )
statement1;
else
statement2;
If the condition is true, statement1 is executed; if the condition is false, statement2 is executed
An else clause can be added to an if statement to make an if-else statement
Remember that if we used curly braces, we could replace statement1 and statement 2 with block1 and block2
One or the other will be executed, but not both

18. Michele Weigle - COMP 14 - Spring 2004
The if-else Statement
if (height <= MAX) {
adjustment = 0; }
else {
adjustment = MAX-height;

19. Michele Weigle - COMP 14 - Spring 2004
Guessing.java Example
Math.random()
returns a random double between 0.0 and 1.0
Generate a random integer between 0-5
int num = (int) (Math.random() * 6);
Generate a random integer between 1-5
int num = (int) (Math.random() * 5) + 1;
0 - 4
1-5

20. Michele Weigle - COMP 14 - Spring 2004
In-Class Exercise
What is the value of adjustment given the following values of height and MAX?
if (height <= MAX) {
adjustment = 0; }
else {
adjustment = MAX-height;
height = 60, MAX = 80
height = 100, MAX = 75
height = 45, MAX = 45
-25

21. Michele Weigle - COMP 14 - Spring 2004
Nested if Statements
The statement (or block) executed as a result of an if statement can be another if statement (nested if).
An else clause is always matched to the closest unmatched if.
Closing curly brace signals the end of an if statement.

22. Michele Weigle - COMP 14 - Spring 2004
Nested if Statements
The general syntax of a nested if statement is:
if (condition1) {
block1 }
else if (condition2) {
block2
else {
block3

23. Michele Weigle - COMP 14 - Spring 2004
Nested if Statements
if (hasFourLegs) {
if (playsFetch) {
System.out.println ("DOG"); }
else {
System.out.println ("CAT");
else if (hasWings) {
System.out.println ("BIRD");
System.out.println ("FISH");
has four legs
plays fetch
doesn't play fetch
Assume here that hasFourLegs, playsFetch, and hasWings are boolean variables
Which if statements match to which else statements?
"else" matches to closest unmatched "if"
notice the indentation
does not have four legs
has wings
doesn't have wings

24. Michele Weigle - COMP 14 - Spring 2004
Min.java Example

25. Michele Weigle - COMP 14 - Spring 2004
The switch Statement

26. Michele Weigle - COMP 14 - Spring 2004
The switch Statement
Provides another means to decide which statement to execute next
Evaluates an expression, then attempts to match the result to one of several possible cases
Each case contains a value and a list of statements
The flow of control transfers to statement associated with the first value that matches

27. Michele Weigle - COMP 14 - Spring 2004
The switch Statement
The general syntax of a switch statement is:
switch ( expression ) {
case value1 :
statement-list1
case value2 :
statement-list2
case value3 :
statement-list3
case ... }
switch
and
case
are
reserved
words
If expression
matches value2,
control jumps
to here
Don't need braces in the statement list

28. Michele Weigle - COMP 14 - Spring 2004
The switch Statement
Expression evaluated must be integral type
integer or character, not boolean or floating point
Case values must be constant (literal), not variable
Can be implemented with nested if statements, but is much clearer with switch statements

29. Michele Weigle - COMP 14 - Spring 2004
The switch Statement
default
no case value matches the expression
if no default exists and no case value matches the expression, no statements in the switch statement are executed
break
processing jumps to statement following the switch statement
usually at the end of each case
Once inside a case, processing continues in order until a break statement is reached

30. Michele Weigle - COMP 14 - Spring 2004
The switch Statement
System.out.print ("Enter prize code: ");
int prize = Integer.parseInt(keyboard.readLine());
switch (prize) {
case 1:
System.out.println (“A Brand New Car!”);
break;
case 2:
System.out.println (“A Trip to Hawaii!”);
default:
System.out.println (“Sorry, Try Again”); }

31. GradeReport.java Example
Michele Weigle - COMP 14 - Spring 2004
GradeReport.java Example

32. Michele Weigle - COMP 14 - Spring 2004
Assume movieRating is an int and movieName is a String
switch (movieRating) {
case 1:
System.out.println ("Run away!");
if (movieName.equals("Gigli")) {
System.out.println ("Quickly!"); }
case 2:
System.out.println ("Save your money");
break;
case 3:
System.out.println ("It's OK");
Questions
What is printed if movieRating is 1 and movieName is "Gigli"?
What is printed if movieRating is 5?
Run away!
Quickly!
Save your money
[Nothing]

33. Michele Weigle - COMP 14 - Spring 2004
if ((x > 0) && (y < 0)) {
z = x+y;
System.out.println (“z = ” + z); }
System.out.print (“The sum is “);
if (x+y < 0) {
System.out.println (“negative.”)
else {
System.out.println (“positive.”);
Questions
What is printed with the following values of x and y:
x = 5, y = -4
x = -9, y = 5
x = 5, y = 5
z=1
The sum is positive.
The sum is negative.
The sum is positive.

34. Suggested Practice Problems
Answers are in back of textbook
Ch 4 (pg. 190): #1, 2, 5, 8, 11

35. Program 2 GUI Calculator
Michele Weigle - COMP 14 - Spring 2004
Program 2 GUI Calculator
Due Wednesday, Feb 18 at 11:59pm
Write a program that performs the operations of a calculator

36. Michele Weigle - COMP 14 - Spring 2004
Next Time in COMP 14
Loops
Reading Assignment: Chapter 5 (pgs )