Computer Programming, Loops using Java

Using Java
MINISTRY OF EDUCATION & HIGHER EDUCATION
COLLEGE OF SCIENCE AND TECHNOLOGY
KHANYOUNIS- PALESTINE
Lecture 9 & 10
Repetition Statements

 Essentials of Counter-Controlled Repetition
 while Repetition Statement
 Example:The average problem
 for Repetition Statement
 Example: Summing the Even Integers from 2 to 20
 do...while Repetition Statement
 break and continue Statements
 Emank X Mezank
2
Presented & Prepared by: Mahmoud R. Alfarra

 A repetition statement (also called a looping
statement or a loop) allows the programmer
to specify that a program should repeat an
action while some condition remains true.
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What is repetition statement ?
While there are more items on my shopping list
Purchase next item and cross it off my list

 Counter-controlled repetition requires:
1. A control variable (or loop counter)
2. The initial value of the control variable
3. The increment (or decrement) by which the
control variable is modified each time through
the loop (also known as each iteration of the
loop)
4. The loop-continuation condition that determines
whether looping should continue.
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Essentials of Counter-Controlled Repetition

 A program can test multiple cases by placing if...else
statements inside other if...else statements to
create nested if...else statements.
5
While Repetition Statement
int x = number;
while (Condition)
{
// actions
x--;
}
Initial variable
The loop-continuation condition,
Can be any other operators
Has a close relation with the
operators and the initial value of x

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Be care
Not providing, in the body of a while statement, an action
that eventually causes the condition in the while to become
false normally results in a logic error called an infinite loop,
in which the loop never terminates.
Set a semi colon after the condition results a logic error

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While Repetition Statement
true
false
Actions
Condition
Start
End
 The while loop is used when you want to test a
condition before entering into the loop.
 The while loop is considered a pretest loop, this allows
you to stop entering the loop even once if the condition
is not true.

 A class of ten students took a quiz. The
grades (integers in the range 0 to 100) for this
quiz are available to you. Determine the class
average on the quiz.
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Example: The average problem
Write the pseudo code and flowchart of the above
example
HW 8.1

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Example: The average problem

 If you want to execute a certain block of code
a specified number of times, use a for loop.
 The syntax of the for loop is as follows:
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for Repetition Statement

Presented & Prepared by: Mahmoud R. Alfarra 11
How to perform repetition using for ?
System.out.println
(counter * 10);

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Be care
Using an incorrect relational operator or an incorrect final
value of a loop counter in the loop-continuation condition of a
repetition statement can cause an off-by-one error.
Using commas instead of the two required semicolons in a
for header is a syntax error.
When a for statement's control variable is declared in the
initialization section of the for's header, using the control
variable after the for's body is a compilation error.
Placing a semicolon immediately to the right of the right
parenthesis of a for header makes that for's body an empty
statement. This is normally a logic error.

 Use a for statement to sum the even integers
from 2 to 20 and store the result in an int
variable called total.
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Example: Summing the Even Integers
Write the pseudo code and flowchart of the above
example
HW 8.2

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Example: Summing the Even Integers
Not using the proper relational operator in the loop-
continuation condition of a loop that counts downward (e.g.,
using i <= 1 instead of i >= 1 in a loop counting down to 1) is
usually a logic error.

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 A person invests $1,000 in a savings account yielding 5%
interest. Assuming that all the interest is left on deposit,
calculate and print the amount of money in the account at
the end of each year for 10 years. Use the following formula
to determine the amounts:
where
• p is the original amount invested (i.e., the principal)
• r is the annual interest rate (e.g., use 0.05 for 5%)
• n is the number of years
• a is the amount on deposit at the end of the nth year.
Home Work
HW 8.3
a = p(1+r)
n

 If you would prefer that the testing of the
loop condition is done after executing the
loop’s code, you would use the post-test
version of the while loop, called the do …
while loop.
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do...while Repetition Statement
Using do..While statement, the body always executes
at least once, but using while statement does not.

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int x = number;
do
{
// actions
x--;
} while (Condition)
Initial variable
The loop-continuation condition,
Can be any other operators
Has a close relation with the
operators and the initial value of x

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true
false
Actions Condition
Start
End

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What is the difference between them ?
 a pretest condition
 can be executed for 0 or more
times
 does not end with semicolon !!!
 a posttest condition
 can be executed for 1 or more
times
 must end with semicolon !!!
while do…while
while (condition)
{
// actions
}
do
{
// actions
}
while (condition);

 Java provides statements break and continue
to alter the flow of control.
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break and continue Statements
.
.
.
break;
Before loop’s block
After loop’s block
.
.
.
continue ;
Before loop’s block
After loop’s block

 The break statement, when executed in a
while, for, do...while or switch, causes
immediate exit from that statement.
 Execution continues with the first statement
after the control statement.
 Common uses of the break statement are to
escape early from a loop or to skip the
remainder of a switch.
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break Statement

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Example: break Statement
All the
iterations
are
completed
from 1 to 4
and in 5’th
iteration
the loop is
broken

 The continue statement, when executed in a
while, for or do...while, skips the remaining
statements in the loop body and proceeds
with the next iteration of the loop.
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continue Statement
In while and do...while statements, the program evaluates
the loop-continuation test immediately after the continue
statement executes.
In a for statement, the increment expression executes, then
the program evaluates the loop-continuation test.

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Example: continue Statement
All the
iterations
are
completed
except
iteration
number 5

‫قال‬
‫تيمية‬ ‫بن‬
:
‫و‬ ‫الدين‬ ‫من‬ ‫اإلسناد‬
‫لقال‬ ‫اإلسناد‬ ‫لوال‬
‫من‬
‫شاء‬ ‫ما‬ ‫شاء‬
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Practices
26

Computer Programming, Loops using Java

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