Computer programming 2 Lesson 8

Computer
Programming 2
Lesson 8– Java – Loop Control
Prepared by: Analyn G. Regaton

LoopControl
A loop statement
allows us to
execute a
statement or
group of
statements
multiple times.

Types of Loop
Sr.No. Loop & Description
1 while loop
Repeats a statement or group of statements while a given
condition is true. It tests the condition before executing the
loop body.
2 for loop
Execute a sequence of statements multiple times and
abbreviates the code that manages the loop variable.
3 do...while loop
Like a while statement, except that it tests the condition at
the end of the loop body.

WHILE LOOP
A while loop statement in Java programming language
repeatedly executes a target statement as long as a given
condition is true.
Syntax
The syntax of a while loop is −
while(Boolean_expression) {
// Statements
}
Here, statement(s) may be a single statement or a block of
statements. The condition may be any expression, and true is
any non zero value.
Boolean_expression = true inside the
loop will be executed
Boolean_expression = false program
control passes to the line immediately to the loop

FLOW
DIAGRAM
Here, key point of
the while loop is that the
loop might not ever run.
When the expression is
tested and the result is
false, the loop body will be
skipped and the first
statement after the while
loop will be executed.

FOR LOOP
The syntax of a for loop is −
for(initialization; Boolean_expression;update) {
// Statements
}
A for loop is a repetition control structure that allows you to
efficiently write a loop that needs to be executed a specific
number of times.
A for loop is useful when you know how many times a task is
to be repeated.

Flow of control
in a for loop
 The initialization step is executed first, and only once.This
step allows you to declare and initialize any loop control
variables and this step ends with a semi colon (;).
 Next, the Boolean expression is evaluated. If it is true, the
body of the loop is executed. If it is false, the body of the loop
will not be executed and control jumps to the next statement
past the for loop.
 After the body of the for loop gets executed, the control
jumps back up to the update statement.This statement
allows you to update any loop control variables.This
statement can be left blank with a semicolon at the end.
 The Boolean expression is now evaluated again. If it is true,
the loop executes and the process repeats (body of loop, then
update step, then Boolean expression). After the Boolean
expression is false, the for loop terminates.

DO-WHILE
A do...while loop is similar to a while loop, except that a
do...while loop is guaranteed to execute at least one time.
Syntax
Following is the syntax of a do...while loop −
do {
// Statements
}
while(Boolean_expression);
Notice that the Boolean expression appears at the end of the
loop, so the statements in the loop execute once before the
Boolean is tested.
If the Boolean expression is true, the control jumps back up to
do statement, and the statements in the loop execute again. This
process repeats until the Boolean expression is false.

LOOP
CONTROL
STATEMENT
Sr.No. Control Statement & Description
1 break statement
Terminates the loop or switch statement and transfers
execution to the statement immediately following the
loop or switch.
2 continue statement
Causes the loop to skip the remainder of its body and
immediately retest its condition prior to reiterating.
Loop control statements change execution from its
normal sequence.When execution leaves a scope, all
automatic objects that were created in that scope are
destroyed.

BREAK
STATEMENT
The break statement in Java programming language
has the following two usages −
•When the break statement is encountered inside a
loop, the loop is immediately terminated and the program
control resumes at the next statement following the
• loop.
•It can be used to terminate a case in the switch
statement (covered in the next chapter).
Syntax
The syntax of a break is a single statement inside any loop −
break;

CONTINUE
STATEMENT
The continue keyword can be used in any of the loop
control structures. It causes the loop to immediately
jump to the next iteration of the loop.
•In a for loop, the continue keyword causes
control to immediately jump to the update
statement.
•In a while loop or do/while loop, control
immediately jumps to the Boolean expression.
Syntax
The syntax of a continue is a single statement inside
any loop −
continue;

PROGRAM
EXAMPLE
Output
10
20
40
50

ENHANCED
for Loop in
Java
As of Java 5, the enhanced for loop was introduced. This is
mainly used to traverse collection of elements including arrays.
Syntax
Following is the syntax of enhanced for loop −
for(declaration : expression) {
// Statements
}
•Declaration − The newly declared block variable, is of a type
compatible with the elements of the array you are accessing.
The variable will be available within the for block and its value
would be the same as the current array element.
•Expression − This evaluates to the array you need to loop
through. The expression can be an array variable or method call
that returns an array.

EXAMPLE
PROGRAM
Output
10, 20, 30, 40, 50,
James, Larry, Tom, Lacy,

Computer programming 2 Lesson 8

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Computer programming 2 Lesson 8