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TOPIC 03
Program Control Structures
SITI HASNAH TANALOL
PM 3, Block A, FKJ
Learning Outcomes
• Upon completion of this lecture, student
should be able to:
• Write expressions using the conditional operator
• Differentiate the Increment and Decrement
operator
• Implement selection control using if, if…else
and switch statements
• Implement repetition control in a program by
using while, do… while and for loop
statements,
Contents
Control structures
Selection
structures
If
if
if..else
Nested if
switch
Loops
Structures
while
do..while
for
Selection Structures
Selection
structures
If
if
if..else
Nested if
switch
if statements
• Example
if(x == y)
System.out.println("X is equal to Y");
if(x != y)
System.out.println("X is not equal to Y"); x = y; System.out.println("However, now it is.");
if (condition)
execute_statements;
if.. Else statements
if(x == y)
System.out.println("X is equal to Y"); else System.out.println("X is NOT equal to Y");
if (condition)
execute_statements;
else
execute_statements;
if(x != y)
System.out.println("X is not equal to Y"); x = y; System.out.println("However, now it is.");
} else {
System.out.println("X is NOT
equal to Y");}
if.. else..if statements
if(x == y)
System.out.println("X is equal to Y"); else if (x !=y) System.out.println("X is NOT equal to Y"); else System.err.println (“ Error Catch!! ");
if (condition)
execute_statements;
else if (condition)
execute_statements;
else
execute_statements;
Nested If statements
if (condition) { if (condition) {
}else if (condition){
}else {
}
}
if (coldOutside==true) { if (snowing==true) { wearParka(); } else { wearJacket(); } } else { wearShorts(); }
Selection Structures
What is the output after executing the following
program?
int mask = 0; int count = 0;
if ((5<7 || (++count <10)) && mask++ <1 ) mask = mask + 1; if (6<8 && false) mask = mask + 10; if( !(mask >1) && ++count>1 ) mask = mask + 100;
System.out.println( " Mask is " + mask + "and count is " + count );
Selection Structures
What is the output after executing the following
program?
int mask = 0; int count = 0;
if (5<7 || ++count <1 && mask++ <1 ) mask = mask + 1; if (6<8 && false) mask = mask + 10; if( !(mask >1) && ++count>1 ) mask = mask + 100;
System.out.println( " Mask is " + mask + " and count is " + count );
Selection Structures
What is the output after executing the following
program?
int n=95;
if (n <= 100) if (n > 90) System.out.println("A"); System.out.println("B"); if (n >80) System.out.println("C"); if (n < 50) System.out.println("D"); else System.out.println("E");
Given that n is :
a) 95
b) 90
c) 45
d) 80
e) 50
The switch Statement The case Statement
3 - 20
- The break statement ends the case statement.
- The break statement is optional.
- If a case does not contain a break , then program
execution continues into the next case.
- The default section is optional and will be
executed if no CaseExpression matches the
SwitchExpression.
3.9 The switch Statement
NoBreaks.java Practice 3
Practice 3: Solution
3.9 The switch Statement
Practice 4
Practice 4 (20 minutes):
A five digit integer is said to be friendly if
- the leftmost digit is divisible by 1
- the leftmost two digits are divisible by 2, the leftmost three digit are
divisible by 3
- the leftmost four digit are divisible by 4, and the leftmost five digits
( the five-digit number itself) is divisible by 5.
For example, the number 42325 is friendly because 4 is divisible by 1,
42 is divisible by 2, 423 is divisible by 3, 4232 is divisible by 4, and 42325
is divisible by 5.
Write a program that prompts for a five-digit integer and determines
whether or not the number is “friendly”. Use JOptionPane for user input
and output.
Compound Assignment Operators
Differences Between Prefix and Postfix
- When an increment or decrement are the only operations
in a statement , there is no difference between prefix and
postfix notation.
- When used in an expression:
- prefix notation indicates that the variable will be incremented or
decremented prior to the rest of the equation being evaluated.
- postfix notation indicates that the variable will be incremented or
decremented after the rest of the equation has been evaluated.
++x
X++
Nested if statements and Multiple Alternative Decisions
What is the output for the following Program.
public static void main (String[] args){
int mask = 5;
if (++mask > 5) System.out.println("mask:"
public static void main (String[] args){ int mask = 2;
if (mask++ > 2) System.out.println("mask:" + mask);
public static void main (String[] args){ int mask = 2;
if (mask++ > 2) System.out.println("mask:" + mask);
public static void main (String[] args){ int mask = 5;
if (mask++ > 5) System.out.println("mask:" + mask);
Loop Structures
Control
structures
Loops
Structures
while
do..while
for
The while Loop
4 - 28
while(condition)
{
statements ;
}
Write a program that use the while loop to print
“Hello” five times.
The while Loop for Input Validation
4 - 29
- Input validation is the process of ensuring that user
input is valid.
System.out.print("Enter a number in the " +
"range of 1 through 100: ");
number = keyboard.nextInt();
// Validate the input.
while (number < 1 || number > 100)
System.out.println("That number is
invalid.");
System.out.print("Enter a number in the " +
"range of 1 through 100: ");
number = keyboard.nextInt();
do…while loops
do
{
statement(s);
}while ( condition );
Practice 9 Solution
Write a program to display the following output.
1
21
321
4321
54321
Practice 9 Solution
Write a program to display the following output.
54321
4321
321
21
1
Nested loops
for(int i = 0; i < 10; i++)
for(int j = 0; j < 10; j++)
loop statement;
for(int i = 0; i < 10; i++){
for(int j = 0; j < 10; j++){
loop statements;
}
}
Nested For Loops
The continue Statement
- The continue statement will cause the currently
executing iteration of a loop to terminate and the
next iteration will begin.
- The continue statement will cause the evaluation
of the condition in while and for loops.
- Like the break statement, the continue
statement should be avoided because it makes the
code hard to read and debug
Problem
- What is the output after executing the following program?
public static void main(String []
args)
{
int i=0;
while ( i < 10 )
{
i++;
if ( i == 5)
break;
System.out.println(i);
}
}
Problem
- What is the output after executing the following program?
public static void main(String [] args)
{
int i=0;
while ( i < 10 )
{
i++;
if ( i == 5)
continue;
System.out.println(i);
}
}
Deciding Which Loops to Use
• The while loop :
- Pretest loop
- Use it where you do not want the statements to execute if
the condition is false in the beginning.
• The do - while loop :
- Post-test loop
- Use it where you want the statements to execute at least one time.
• The for loop:
- Pretest loop
- Use it where there is some type of counting variable that
can be evaluated.
The Random Class
4 - 45
• Some applications, such as games and simulations,
require the use of randomly generated numbers.
• The Java API has a class, Random, for this purpose.
To use the Random class, use the following
import statement and create an instance of the
class.
4.11 The Random Class
import java.util.Random;
Random randomNumbers = new Random();
Some Methods of the
Random Class
4 - 46
Method Description
nextDouble() Returns the next random number as a double. The number will be within the range of 0.0 and 1.0.
nextFloat() Returns the next random number as a float. The number will be within the range of 0.0 and 1.0.
nextInt() Returns the next random number as an int. The number will be within the range of an int, which is – 2,147,483, to +2,147,483,648.
nextInt(int n) (^) This method accepts an integer argument, n. It returns a random number as an int. The number will be within the range of 0 to n.
4.11 The Random Class
Random Class
Thank You !!
”Effort always is a best Indicator of Interest”
