Repetition Statements

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Lecture 3-1

• Repetition Statements

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Objectives

• Implement repetition control in a program using
  while statements.
• Implement repetition control in a program using
  dowhile statements.
• Implement repetition control in a program using
  for statements.
• Nest a loop repetition statement inside another
  repetition statement.
• Choose the appropriate repetition control
  statement for a given task.
• Prompt the user for a yesno reply using the
  ResponseBox class from the javabook package.
• Output formatted data using the Format class from
  the javabook package.

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The while Statement
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Example Testing Input Data

• Heres a realistic example of using the while
  loop to accept only the valid input data.
• Accepts age between 0 and 130, exclusively.

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while Loop Pitfall - 1
Infinite Loops Both loops will not terminate
because the boolean expressions will never become
false.
Note With JAVA an Overflow Error (due to an
attempt to assign a value larger than the maximum
value a variable can hold) will not terminate a
program
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while Loop Pitfall - 2
Using Real Numbers Loop 2 terminates, but Loop 1
does not because only an approximation of a real
number can be stored in a computer memory.
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while Loop Pitfall - 3

• Goal Execute the loop body 10 times.

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Checklist for Repetition Control

• Watch out for the off-by-one error (OBOE).
• Make sure the loop body contains a statement that
  will eventually cause the loop to terminate.
• Make sure the loop repeats exactly the correct
  number of times.
• If you want to execute the loop body N times,
  then initialize the counter to 0 and use the test
  condition counter lt N or initialize the counter
  to 1 and use the test condition counter lt N.

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Useful Shorthand Operators
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The do-while Statement
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do-while Statement
do ltstatementgt while ( ltboolean expressiongt )
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Loop Control without Boolean Variable
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Loop Control with Boolean Variable
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Question-5

• Rewrite the following while loop as a do-while
  loop.
• int count0, sum0
• while (countlt10)
• sum count
• count
• Answer
• int count0, sum0
• do
• sum count
• count
• while (countlt10)

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ResponseBox

• The ResponseBox class is used to get a YES or NO
  response from the user.

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ResponseBox Processing the Selection

• To determine which button the user clicked, we
  write

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ResponseBox Sample Usage

• Heres a typical use of ResponseBox

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ResponseBox Other Usage

• ResponseBox can have up to three buttons with
  user-designated labels.

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ResponseBox Methods
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The for Statement
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Syntax for the for Statement
for ( ltinitializationgt ltboolean expressiongt
ltincrementgt ) ltstatementgt
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More Examples
i 0, 5, 10, , 95
j 2, 4, 8, 16, 32
k 100, 99, 98, 97, ..., 1
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The Nested-for Statement

• Nesting a for statement inside another for
  statement is commonly used technique in
  programming.
• Lets generate the following table using
  nested-for statement.

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Generating the Table
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Question-6

• What will be the value of sum after the following
  nested-for loop is executed
• int sum0
• for (int i0 ilt5 i)
• sumsumi
• for (int ji jlt5 j)
• sumsumj
• Answer 50 (How?)

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Formatting Integers
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Formatting Real Numbers
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Formatting Strings
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Methods in The Format Class