1. Chapter 5: Control Structures II
Java Programming:
Program Design Including Data Structures

2. Chapter Objectives Learn about repetition (looping) control structures
Explore how to construct and use:
count-controlled,
sentinel-controlled,
flag-controlled, and
EOF-controlled
repetition structures
Examine break and continue statements
Discover how to form and use nested control structures
Java Programming: Program Design Including Data Structures

3. Why Is Repetition Needed?
Many situations require the same statement(s) to be executed several times
Example:
Finding average grades for students in a class
Processing a batch of purchase orders
Explore a solution space until a given pattern is found
Refining the solution of a problem by successive approximation to the optimum response.
Java Programming: Program Design Including Data Structures

4. The while Looping (Repetition) Structure
Syntax:
while (expression)
statement
Expression is always true in an infinite loop
Statements must change value of expression to false
Java Programming: Program Design Including Data Structures

5. The while Looping (Repetition) Structure (continued)
Example 5-1
i = 0; //Line 1
while (i <= 20) //Line 2 {
System.out.print(i + " "); //Line 3
i = i + 5; //Line 4 }
System.out.println(); //Line 5
Output
Java Programming: Program Design Including Data Structures

6. The while Looping (Repetition) Structure (continued)
while loops are written in the following form:
//initialize the loop control variable(s)
while (expression) //expression tests control
{ //variable .
//update the loop control variable(s) }
Java Programming: Program Design Including Data Structures

7. Counter-Controlled while Loop
Used when exact number of entry pieces is known
General form:
int N = //value input by user or specified
//in program
int counter = 0;
while (counter < N) { .
counter++; }
Java Programming: Program Design Including Data Structures

8. Sentinel-Controlled while Loop
Used when exact number of entry pieces is unknown, but last entry (special/sentinel value) is known
General form:
Input the first data item into variable;
while (variable != sentinel) { .
input a data item into variable; }
Java Programming: Program Design Including Data Structures

9. Flag-Controlled while Loop
Boolean value used to control loop
General form:
boolean found = false;
while (!found) { .
if (expression)
found = true; }
Java Programming: Program Design Including Data Structures

10. EOF (End of File)-Controlled while Loop
Used when input is from files
Sentinel value is not always appropriate
In an EOF-controlled while loop that uses the Scanner object console to input data, console acts at the loop control variable
Java Programming: Program Design Including Data Structures

11. EOF (End of File)-Controlled while Loop (continued)
The method hasNext, of the class Scanner, returns true if there is an input in the input stream; otherwise, it returns false
The expression console.hasNext() acts as the loop condition
Expressions such as console.nextInt() update the value of the loop condition
Java Programming: Program Design Including Data Structures

12. EOF-Controlled while Loop (continued)
General form of the EOF-controlled while loop that uses the Scanner object console to input data:
while (console.hasNext()) {
//Get the next input and store in an
//appropriate variable
//Process data }
Java Programming: Program Design Including Data Structures

13. EOF-Controlled while Loop (continued)
Suppose that inFile is a Scanner object initialized to the input file. In this case, the EOF-controlled while loop takes the following form:
while (inFile.hasNext()) {
//Get the next input and store in an
//appropriate variable
//Process data }
Java Programming: Program Design Including Data Structures

14. Programming Example: Checking Account Balance
Input file: Customer’s account number, account balance at beginning of month, transaction type (withdrawal, deposit, interest), transaction amount
Output: Account number, beginning balance, ending balance, total interest paid, total amount deposited, number of deposits, total amount withdrawn, number of withdrawals
Java Programming: Program Design Including Data Structures

15. Programming Example: Checking Account Balance (continued)
Solution:
Read data
EOF-controlled loop
switch structure of transaction types
Determine action (add to balance or subtract from balance depending on transaction type)
Java Programming: Program Design Including Data Structures

16. Programming Example: Fibonacci Number
Fibonacci formula for any Fibonacci sequence:
an = an-1 + an-2
Input: First two Fibonacci numbers in sequence, position in sequence of desired Fibonacci number (n)
int previous1 = Fibonacci number 1
int previous2 = Fibonacci number 2
int nthFibonacci = Position of nth Fibonacci number
Output: nth Fibonacci number
Java Programming: Program Design Including Data Structures

17. Programming Example: Fibonacci Number (Solution)
if (nthFibonacci == 1)
current = previous1;
else if (nthFibonacci == 2)
current = previous2;
else {
counter = 3;
while (counter <= nthFibonacci)
current = previous2 + previous1;
previous1 = previous2;
previous2 = current;
counter++; }
Java Programming: Program Design Including Data Structures

18. The for Looping (Repetition) Structure
Specialized form of while loop
Simplifies the writing of count-controlled loops
Syntax:
for (initial statement; loop condition;
update statement)
statement
Java Programming: Program Design Including Data Structures

19. The for Looping (Repetition) Structure (continued)
Execution:
Initial statement executes
Loop condition is evaluated
If loop condition evaluates to true, execute for loop statement and execute update statement
Repeat until loop condition is false
Java Programming: Program Design Including Data Structures

20. The for Looping (Repetition) Structure (continued)
Java Programming: Program Design Including Data Structures

21. The for Looping (Repetition) Structure (continued)
Example 5-8
The following for loop prints the first 10 nonnegative integers:
for (i = 0; i < 10; i++)
System.out.print(i + " ");
System.out.println();
Java Programming: Program Design Including Data Structures

22. The for Looping (Repetition) Structure (continued)
Example 5-9
The following for loop outputs the word Hello and a star (on separate lines) five times:
for (i = 1; i <= 5; i++) {
System.out.println("Hello");
System.out.println("*"); }
Java Programming: Program Design Including Data Structures

23. The for Looping (Repetition) Structure (continued)
2. The following for loop outputs the word Hello five times and the star only once:
for (i = 1; i <= 5; i++)
System.out.println("Hello");
System.out.println("*");
Java Programming: Program Design Including Data Structures

24. The for Looping (Repetition) Structure (continued)
Does not execute if initial condition is false
Update expression changes value of loop control variable, eventually making it false
If loop condition is always true, result is an infinite loop
Java Programming: Program Design Including Data Structures

25. The for Looping (Repetition) Structure (continued)
Infinite loop can be specified by omitting all three control statements
If loop condition is omitted, it is assumed to be true
for statement ending in semicolon is empty
Java Programming: Program Design Including Data Structures

26. Programming Example: Classify Numbers
Input: N integers (positive, negative, and zeros)
int N = 20; //N easily modified
Output: Number of 0s, number of even integers, number of odd integers
Java Programming: Program Design Including Data Structures

27. Programming Example: Classify Numbers (Solution)
for (counter = 1; counter <= N; counter++) {
number = console.nextInt();
System.out.print(number + " ");
switch (number % 2)
case 0: evens++;
if (number == 0)
zeros++;
break;
case 1:
case -1: odds++;
} //end switch
} //end for loop
Java Programming: Program Design Including Data Structures

28. The do…while Loop (Repetition) Structure
Syntax: do
statement
while (expression);
Statements are executed before expression
Statements are executed at least once and then continued if expression is true
Java Programming: Program Design Including Data Structures

29. do…while Loop (Post-Test Loop)
Java Programming: Program Design Including Data Structures

30. break Statements Used to exit early from a loop
Used to skip remainder of switch structure
Can be placed within if statement of a loop
If condition is met, loop is exited immediately
Java Programming: Program Design Including Data Structures

31. continue Statements Used in while, for, and do...while structures
When executed in a loop:
Remaining statements in the loop are skipped
Proceeds with the next iteration of the loop
When executed in a while/do…while structure, expression is evaluated after continue
In a for structure, the update statement is executed after continue; the loop condition then executes
Java Programming: Program Design Including Data Structures

32. Nested Control Structures
Provides new power, subtlety, and complexity
if, if…else, and switch structures can be placed within while loops
for loops can be found within other for loops
Java Programming: Program Design Including Data Structures

33. Nested Control Structures (Example)
for (int i = 1; i <= 5; i++) {
for (int j = 1; j <= i; j++)
System.out.print(" *");
System.out.println(); }
Output: * **
***
****
*****
Java Programming: Program Design Including Data Structures

34. Chapter Summary Looping mechanisms: Nested control structures
Counter-controlled while loop
Sentinel-controlled while loop
Flag-controlled while loop
EOF-controlled while loop
for loop
do…while loop
break statement
continue statement
Nested control structures
Java Programming: Program Design Including Data Structures