1. Computer Programming with Java
Chapter 3
Flow of Control

2. Contents Overview Branching Statements Loop Statements
Programming with Loops

3. Overview Flow of control
the order in which actions are performed by your program.
Branching statements
choose one action from a list of two or more possible actions
Loop statements
repeats some action again and again until some stopping condition is met

4. Branching Statements The if-else- statement if (Boolean_Expression)
If the Boolean_Expression is true, then Statement_1 is executed;
otherwise, Statement_2 is executed.

5. public class BankBalance{
public static final double OVER_DRAWN_PENALTY = 8.00;
public static final double INTEREST_RATE = 0.02;//2% annually
public static void main(String[] args)
double balance;
System.out.print("Enter your checking account balance: $");
balance = SavitchIn.readLineDouble();
System.out.println("Original balance $" + balance);
if (balance >= 0)
balance = balance + (INTEREST_RATE * balance)/12;
else
balance = balance - OVER_DRAWN_PENALTY;
System.out.println("After adjusting for one month");
System.out.println("of interest and penalties,");
System.out.println("your new balance is $" + balance); }
Display 3.1: A Program using if-else

6. Branching Statements (1)
Comparison Operators

7. public class StringEqualityDemo{
public static void main(String[] args){
String s1, s2;
System.out.println("Enter two lines of text:");
s1 = SavitchIn.readLine();
s2 = SavitchIn.readLine();
if (s1.equals(s2))
System.out.println("The two lines are equal.");
else
System.out.println("The two lines are not equal.");
if (s2.equals(s1))
if (s1.equalsIgnoreCase(s2))
System.out.println("But, the lines are equal ignoring case.");
System.out.println("Lines are not equal even ignoring case."); }
Display 3.3: Testing Strings for Equality

8. Branching Statements (2)
Boolean Expression
an expression that is either true or false.
“and”: &&
When you form a larger boolean expression by connecting two smaller expression with &&, the entire larger expression is true provided that both of the smaller expressions are true.
(sub_expression1) && (sub_expression2)
e.g.)
if ((pressure > min) && (pressure < max))
System.out.println(“Pressure is OK.”);
else
System.out.println(“Warning: Pressure is out of range.”);

9. Branching Statements (3)
“or”
the meaning is essentially the same as the word “or”
(sub_expression1) || (sub_expression2)
e.g.)
if ((salary > expenses) || (savings > expenses))
System.out.println(“Solvent.”);
else
System.out.println(“Bankrupt.”);

10. && (and)
|| (or)
! (not)
Display 3.12: Truth tables for boolean operators

11. Branching Statements (4)
Nested statements
an if-else statement contains two smaller statements within it.
Compound statements
these statements formed by enclosing a list of statements within curly brackets.
Rule of thumb
To eliminate some confusion in the nested if-else statements, you had better use curly brackets to group things.

12. Nested statements
if (balance >= 0)
if (INTEREST_RATE >= 0)
balance = balance + (INTEREST_RATE * balance)/12;
else
System.out.println(“Cannot have a negative interest.”);
balance = balance - OVER_DRAWN_PENALTY;
Compound statements
if(balance >= 0){
System.out.println(“Good for you. You earned interest.”);
balance = balance + (INTEREST_RATE * balance) /12;
}else{
System.out.println(“You will be charged a penalty.”); }

13. Branching Statements (4)
Multibranch if-else statements
you can use nested if-else statements to produce multiway branches that branch into any number of possibilities.
If ( Boolean_Expression1)
Action1
else if ( Boolean_Expression2)
Action2 …
else if ( Boolean_Expression n)
Action n
else
Default_Action
if (balance >= 0)
System.out.println(“Positive balance.”);
else if (balance < 0)
System.out.println(“Negative balance.”);
else if (balance == 0)
System.out.println(“Zero balance.”);

14. public class Grader{
public static void main(String[] args){
int score;
char grade;
System.out.println("Enter your score: ");
score = SavitchIn.readLineInt();
if (score >= 90)
grade = 'A';
else if (score >= 80)
grade = 'B';
else if (score >= 70)
grade = 'C';
else if (score >= 60)
grade = 'D';
else
grade = 'F';
System.out.println("Score = " + score);
System.out.println("Grade = " + grade); }
Display 3.4: Multibranch if-else-Statement

15. Branching Statements (5)
The switch statement
a multiway branch that makes its decision on which way to branch based on the value of an integer or character expression
switch (Controlling_Expression){
case Case_Label:
statement; … break; …
default: }

16. public class MultipleBirths{
public static void main(String[] args){
int numberOfBabies;
System.out.print("Enter number of babies: ");
numberOfBabies = SavitchIn.readLineInt();
switch (numberOfBabies){
case 1:
System.out.println("Congratulations."); break;
case 2:
System.out.println("Wow. Twins."); break;
case 3:
System.out.println("Wow. Triplets."); break;
case 4:
case 5:
System.out.println("Unbelieveable.");
System.out.println(numberOfBabies + " babies"); break;
default:
System.out.println("I don't believe you.");
break; }
Display 3.5: A switch-Statement

17. Loop Statements Program often need to repeat some action. Terminology
loop: A portion of a program that repeats a statement or group of statements
body: the statement (or group of statements) to be repeated in a loop
iteration: each repetition of the loop body
infinite loop: A loop that iterates its body repeatedly without ever ending
see text p116.

18. General structure of a Loop
initializing statements
loop body
mechanism for ending the loop
Rule of thumb
When you design a loop, you need to determine what action the body of the loop will take and you need to determine a mechanism for deciding when the loop should stop repeating the loop body.
How do you decide whether to use one of loop statements?
See text p 124: Choosing a Loop statement

19. Loop Statements (1) while statements
repeats its action again and again until a controlling boolean expression becomes false.
Note that the body of a while-loop can be executed zero times.
while(Boolean_Controlling_Expression){
Body }
The Body may be either a simple statement or more likely, a compound statement consisting of a list of statements enclosed in curly brackets {}.

20. public class WhileDemo { public static void main(String[] args)
int count, number;
System.out.println("Enter a number");
number = SavitchIn.readLineInt();
count = 1;
while (count <= number)
System.out.print(count + ", ");
count++; }
System.out.println();
System.out.println("Buckle my shoe.");
Display 3.6: A while-Loop

21. Loop Statements (2) do-while statement
very similar to the while-statement, but the loop body of do-while statement is always executed at least once.
do {
Body
}while(Boolean_Controlling_Expression);
The Body may be either a simple statement or more likely, a compound statement consisting of a list of statements enclosed in curly brackets {}.

22. public class DoWhileDemo { public static void main(String[] args)
int count, number;
System.out.println("Enter a number");
number = SavitchIn.readLineInt();
count = 1; do
System.out.print(count + ", ");
count++;
}while (count <= number);
System.out.println();
System.out.println("Buckle my shoe."); }
Display 3.7: A do-while-Loop

23. Display 3.8: Roach Population Program
public class BugTrouble{
public static final double GROWTH_RATE = 0.95;//95% per week
public static final double ONE_BUG_VOLUME = 0.002;//cubic feet
public static void main(String[] args){
System.out.println("Enter the total volume of your house");
System.out.print("in cubic feet: ");
double houseVolume = SavitchIn.readLineDouble();
System.out.println("Enter the estimated number of");
System.out.print("roaches in your house:");
int startPopulation = SavitchIn.readLineInt();
int countWeeks = 0;
double population = startPopulation;
double totalBugVolume = population*ONE_BUG_VOLUME;
while (totalBugVolume < houseVolume){
population = population + (GROWTH_RATE*population);
totalBugVolume = population*ONE_BUG_VOLUME;
countWeeks++; }
Display 3.8: Roach Population Program

24. System.out.println("Starting with a roach population of ” + startPopulation);
System.out.println("and a house with a volume of " + houseVolume + " cubic feet,");
System.out.println("after " + countWeeks + " weeks,");
System.out.println("the house will be filled");
System.out.println("floor to ceiling with roaches.");
System.out.println("There will be " + (int)population + " roaches.");
System.out.println("They will fill a volume of " + (int)totalBugVolume + " cubic feet");
System.out.println("Better call Debugging Experts Inc."); }

25. Loop Statements (3) for-statement
a specialized loop statement that allows you to easily convert pseudocode (see text p. 129)
for(Initializing_Action; Boolean_Expression; Action_After_Each_Iteration){
Body }
The Body may be either a simple statement or more likely, a compound statement consisting of a list of statements enclosed in curly brackets
Do the following for each value of count from 1 to 3:
System.out.println(count);
System.out.println(“Go”);

27. public static void main(String[] args)
public class ForDemo {
public static void main(String[] args)
int countDown;
for (countDown = 3; countDown >= 0; countDown--)
System.out.println(countDown);
System.out.println("and counting."); }
System.out.println("Blast off!");
Display 3.9: A for-statement

28. Loop Statements (4) break-statement exit Method
if you want to end a loop in the middle of the loop body
exit Method
an invocation of the exit method ends the program.
0: a normal termination
1: abnormal termination
e.g.) System.exit(0);

29. public class BreakDemo{
public static void main(String[] args) {
int itemNumber;
double amount, total;
System.out.println("You may buy ten items, but");
System.out.println("the total price must not exceed $100.");
total = 0;
for (itemNumber = 1; itemNumber <= 10; itemNumber++) {
System.out.print("Enter cost of item #" + itemNumber + ": $");
amount = SavitchIn.readLineDouble();
total = total + amount;
if (total >= 100) {
System.out.println("You spent all your money.");
break; }
System.out.println("Your total so far is $" + total);
System.out.println("You may purchase up to "+ (10 - itemNumber) + "more items.");
System.out.println("You spent $" + total);
Display 3.10: Ending a loop with a break-statement