Branching Statements Simple if statement if-else statement if-elseif-else statement switch statement Block statement Nested if statements

1. CS 120 - Programming I
Lecture 5 : Flow of Control
Branching Mechanism
Jubail Industrial College
Computer Science & Engineering Department

2. 2
• Branching Statements
oSimple if statement
oif-else statement
oif-elseif-else statement
oswitch statement
• Block statement
• Nested if statements
Outline

3. Branching statements
• Sometimes a single (or block) statement needs to be executed if a certain
condition exists.
• A branching statement is used for this purpose, and it is controlled by a
Boolean expression (true/false).
• There are mainly the following types of branching statements:
o Simple if.
o If-else.
o Multiway if-else (If-elseif-else)
o Nested if-else.
o switch.

4. Simple if Statement …
• General structure:
• If the boolean_expression is true, then the block_statement is executed. Otherwise, it
will NOT be executed.

5. Simple if Statement …
Control Flow of if:

6. • The if-else statement is used if an alternative action need to be done in case the
condition is false.
• General structure:
if ( boolean_expression ){
then_block
}
else {
else_block
}
Executed when boolean_expression true
Executed when boolean_expression false
if-else Statement …

7. if-else Statement
• Example:
System.out.print(“Enter two numbers: “);
int n1 = k.nextInt();
int n2 = k.nextInt();
if ( n1 > n2 ){
System.out.println(n1 + “ is greater than ” + n2);
}
else {
System.out.println(n1 + “ is not greater than ” + n2);
}
What is printed if n1 = n2?

8. if-elseif-else Statement …
• This statement is used for multiple alternative actions based on different
conditions. It is used when a single block needs to be executed from several blocks.
• General structure: if (condition-1)
BLOCK1
else if (condition-2)
BLOCK2
else if (condition-3)
BLOCK3
...
else if (condition-n)
BLOCKn
else
BLOCKn+1
Optional
Block i is executed if
its condition-i is true
It is executed if all
conditions are false
conditions are
evaluated from
top to bottom

9. if-elseif-else Statement …
• The following code prints appropriate message based on the following
table:
System.out.print("Enter your score: ");
int score = k.nextInt();
if (score >= 85)
System.out.println("Grade is A");
else if (score >= 75)
System.out.println("Grade is B");
else if (score >= 65)
System.out.println("Grade is C");
else if (score >= 50)
System.out.println("Grade is D");
else
System.out.println("Grade is N");
Test Score Grade
85  score A
75  score  85 B
65  score  75 C
50  score  65 D
score  50 N

10. The switch Statement
• The switch statement is the only other kind of Java statement that
implements multiway branching.
• When a switch statement is evaluated, one of a number of different
branches is executed.
• The choice of which branch to execute is determined by a controlling
expression enclosed in parentheses after the keyword switch
• The controlling expression must evaluate to a char, int, short, or byte and
each label is of the same type.

11. The switch Statement
• Each branch statement in a switch statement starts with the
reserved word case, followed by a constant called a case
label, followed by a colon, and then a sequence of statements
• Each case label must be of the same type as the controlling
expression
• Case labels need not be listed in order or span a complete interval,
but each one may appear only once
• Each sequence of statements may be followed by a break
statement ( break;)

12. • There can also be a section labeled default:
• The default section is optional, and is usually last
• Even if the case labels cover all possible outcomes in a given switch
statement, it is still a good practice to include a default section
• It can be used to output an error message, for example
• When the controlling expression is evaluated, the code for the
case label whose value matches the controlling expression is
executed
• If no case label matches, then the only statements executed are those
following the default label (if there is one)
The switch Statement

13. The switch Statement
• The switch statement ends when it executes a break statement,
or when the end of the switch statement is reached
• When the computer executes the statements after a case label, it
continues until a break statement is reached
• If the break statement is omitted, then after executing the code for one
case, the computer will go on to execute the code for the next case
• If the break statement is omitted inadvertently, the compiler will not
issue an error message

14. switch (Controlling_Expression)
{
case Case_Label_1:
Statement_Sequence_1
break;
case Case_Label_2:
Statement_Sequence_2
break;
case Case_Label_n:
Statement_Sequence_n
break;
default:
Default_Statement Sequence
break;
}
The Switch Statement

15. double y = 30, z = 20;
Scanner kb = new Scanner(System.in);
System.out.println("1. add ");
System.out.println("2. Subtract ");
System.out.println("3. Multiply ");
System.out.print("Enter a value:");
int choice = kb.nextInt();
switch (choice) {
case 1: System.out.println(z + y);
break;
case 2: System.out.println(z - y);
case 3: System.out.println(z * y);
break;
default: System.out.println("Wrong Choice.");
}
break;
Enter a value: 2
-10
Enter a value: 65
Wrong Choice.
If omitted
Enter a value: 2
-10
600
The Switch Statement

16. Block Statement (Compound statement)
• A block statement consists of one or more Java statements enclosed in braces.
• Example of a block statement:
{
statement 1;
statement 2;
…
statement n;
}
• It is used to group a number of statements to be done under certain condition.
• A block statement is treated like a single statement.

17. Block Statement (Compound statement)
• Use braces if the <then> or <else> block has more than 1 statement. If only one
statement is there braces are optional.
System.out.print("Enter two numbers: ");
int x = k.nextInt(), y = k.nextInt(), d;
if ( x > y )
d = x – y;
System.out.println("The difference = " + d);
else
d = y – x;
System.out.println("The difference = " + d);
if ( x > y ){
d = x – y;
}else{
d = y – x;
System.out.println(“The difference = “ + d);}
Error
Correct

18. Nested if Statement
• An if statement can be inside another if statement.
• The inner if statement is executed when the enclosing block statement is
executed.
• Always use indentation with nested if statements for better readability.
if (salary >= 5000) {
if (months >= 3) {
System.out.println("You get 50000 loan");
} else {
System.out.println("You get 20000 loan");
}
} else {
System.out.println("You cannot get a loan");
}

19. if (x < y) {
if (x < z)
System.out.println("Hello");
} else {
System.out.println("Good bye");
}
Equivalent to
if (x < y) {
if (x < z) {
System.out.println("Hello");
}
} else {
System.out.println("Good bye");
}
This if is executed only
when x < y is true.
Nested simple if

20. Nested if-else
Equivalent to
• In nested if statements when there is no braces, else is associated with the closest if.
if (x < y)
if (x < z)
System.out.println("Hello");
else
System.out.println("Good bye");
if (x < y) {
if (x < z) {
System.out.println("Hello");
}
else {
System.out.println("Good bye");
}
}
This if-else is executed only when x < y
is true.

21. Nested if-else
• Convert the following diagram into Java code.
pH > 7
pH < 12
pH is 7
pH > 2
True
False
‘Very
acidic’
False
False
‘Acidic’
True
‘Neutral’
True
‘Very
alkaline’
False ‘Alkaline’
True

22. Exercises
1.Write a Java program that reads an integer using Scanner then
tests if it is odd or even.
The format of the input and output should be as follows:
Please enter a number: 10
10 is even.
2.Write a program that reads three integers and prints them in
increasing order. Example:
Please enter three integers: 9 21 5
The integers in increasing order are: 5 9 21

23. 3.Write a program that reads an integer between 0 and 10
and
then prints the word corresponding to the number. Example:
Please enter a number between 0 and 10: 7
You entered: seven
Exercises

24. The
end