Iterative Statements in Java ICSE Class 9: Loops, break and continue

What Iterative Statements in Java is about

Weightage: CISCE publishes no chapter weightage and no question-paper layout for ICSE Class 9 Computer Applications. Class IX is examined by your school: one 100-mark theory paper of 2 hours, plus 100 marks of internal assessment (at least 15 programming assignments and a written project on ethical computing). This is topic 9 of the 2028 syllabus.Source: CISCE ICSE 2028 Computer Applications syllabus, Class IX

Key concepts

Why loops and the parts of a loop

A loop repeats a set of statements (the body) as long as a test condition is true. Each repetition is an iteration.

Why loops are needed: to print the multiplication table of 7 without loops needs 10 println statements; with a loop it needs one statement inside a for. For 1,000 values the saving is enormous, and the number of repetitions can be decided at run time (for example, a number entered by the user).

Every loop has four parts:
1. Initialisation: gives the loop control variable its starting value (int i = 1).
2. Test condition: decides whether to continue (i <= 10).
3. Body: the statements repeated.
4. Update (increment/decrement): changes the control variable so that the condition eventually becomes false (i++).

Types:

• Entry-controlled (pre-tested) loops test the condition before the body: for and while. If the condition is false at the start, the body runs zero times.
• Exit-controlled (post-tested) loop tests after the body: do-while. The body always runs at least once.

Worked example

(2 marks) Distinguish between entry-controlled and exit-controlled loops with an example of each.

Try it first, then show the solutionSolution

1. Entry-controlled: condition checked before the body; may run zero times; for, while - 1 mark.
2. Exit-controlled: condition checked after the body; runs at least once; do-while - 1 mark.

Answer: An entry-controlled loop (for, while) tests its condition before executing the body, so the body may not run at all. An exit-controlled loop (do-while) tests after the body, so the body runs at least once.

The for loop

Syntax:
for (initialisation; test condition; update)
{
body;
}
Order of execution: initialisation once → test → body → update → test → body → update ... until the test is false.

Use for when the number of iterations is known in advance.

Examples (as run in this study guide):

• Factorial: long f = 1; for (int i = 1; i <= 6; i++) f = f * i; gives 6! = 720.
• Counting iterations: for (int i = 10; i > 0; i -= 3) prints 10 7 4 1: 4 times.
• Sum of even numbers 2 to 20: for (int i = 2; i <= 20; i += 2) es += i; gives 110.
• Series: double s = 0; for (int i = 1; i <= 5; i++) s = s + 1.0 / i; gives s = 2.283333333333333 (1.0 / i avoids integer division).

The control variable after the loop: int p; for (p = 1; p <= 5; p++); leaves p = 6, the first value that failed the test (the semicolon makes the body empty).

Worked example

(2 marks) How many times does this loop run, and what does it print? for (int i = 10; i > 0; i -= 3) System.out.print(i + " ");

Try it first, then show the solutionSolution

1. i takes 10, 7, 4, 1; next value −2 fails i > 0 - 1 mark.
2. Runs 4 times; prints 10 7 4 1 - 1 mark.

Answer: 4 times; output: 10 7 4 1

The while and do-while loops

while loop (entry-controlled):
initialisation;
while (condition)
{
body;
update;
}
Use while when the number of iterations is not known in advance, for example processing the digits of a number until it becomes 0.

do-while loop (exit-controlled):
initialisation;
do
{
body;
update;
} while (condition); // note the semicolon
Use do-while when the body must run at least once, for example showing a menu before asking whether to continue.

Difference shown by code (as run in this study guide):
int x = 10; do { System.out.println("x = " + x); x++; } while (x < 5); prints x = 10 once.
int y = 10; while (y < 5) { System.out.println("y = " + y); y++; } prints nothing; y stays 10.

Digit processing pattern (while):
while (copy > 0)
{
int d = copy % 10; // last digit
sum = sum + d;
rev = rev * 10 + d;
copy = copy / 10; // remove last digit
}
For 4729: digits 9, 2, 7, 4; sum = 22; reverse = 9274.

Worked example

(2 marks) State two differences between while and do-while.

Try it first, then show the solutionSolution

1. while tests before the body (entry-controlled); do-while tests after (exit-controlled) - 1 mark.
2. while may run zero times; do-while runs at least once; do-while ends with a semicolon after while(condition) - 1 mark.

Answer: (1) while checks the condition before the body, whereas do-while checks it after the body. (2) A while loop may not execute at all, but a do-while loop executes at least once (and its syntax ends with while (condition);).

Inter-conversion of loops

Any loop can be rewritten as another. Move the parts carefully.

Printing 1 to 5 (all three as run in this study guide, each printing 1 2 3 4 5):
for:
for (int i = 1; i <= 5; i++)
System.out.print(i + " ");

while:
int i = 1;
while (i <= 5)
{
System.out.print(i + " ");
i++;
}

do-while:
int i = 1;
do
{
System.out.print(i + " ");
i++;
} while (i <= 5);

Steps for conversion from for: put the initialisation before the loop; put the condition in while( ); put the update as the last statement of the body.

Caution: converting to do-while changes behaviour if the condition is false at the start (do-while still runs once). Conversion is exact only when the first test is true.

Worked example

(2 marks) Convert to a while loop: for (int k = 20; k >= 5; k -= 5) System.out.println(k);

Try it first, then show the solutionSolution

1. Initialisation before the loop: int k = 20; condition in while: while (k >= 5) - 1 mark.
2. Body then update inside braces: { System.out.println(k); k -= 5; } - 1 mark.

Answer: int k = 20;
while (k >= 5)
{
System.out.println(k);
k -= 5;
}

Variations: multiple counters, infinite and delay loops

Multiple counter variables: a for loop can initialise and update several variables, separated by commas.
for (int i = 1, j = 10; i < j; i += 2, j -= 2)
System.out.print(i + "," + j + " ");
As run: 1,10 3,8 5,6 (stops when i = 7, j = 4).

Finite loop: ends after a fixed number of iterations.
Infinite loop: never ends on its own because the condition never becomes false.

• for (;;) { } , while (true) { } , or a forgotten update such as int i = 1; while (i <= 5) System.out.println(i);
• Infinite loops are usually errors, but are useful with break: int k = 1; for (;;) { k = k * 3; if (k > 100) break; } gives k = 243 (as run).

Delay loop: a loop with an empty body, used to create a pause by making the computer count:
for (long t = 1; t <= 100000000L; t++);
The semicolon after the header means the body is empty. The length of the delay depends on the speed of the computer, so it is not precise.

Empty-body trap: for (p = 1; p <= 5; p++); System.out.println(p); prints 6 once, because the semicolon ended the loop.

Worked example

(2 marks) Give the output: int k = 1; for (;;) { k = k * 3; if (k > 100) break; } System.out.println("k = " + k);

Try it first, then show the solutionSolution

1. k becomes 3, 9, 27, 81, 243 - 1 mark.
2. 243 > 100, so break exits the infinite loop: k = 243 - 1 mark.

Answer: k = 243

Jump statements: break and continue

break: ends the loop immediately; control passes to the first statement after the loop. (It also ends a switch.)
continue: skips the rest of the current iteration and goes on to the next iteration (in a for loop, to the update; in while and do-while, to the condition).

As run in this study guide:
for (int i = 1; i <= 10; i++)
{
if (i % 3 == 0) continue;
if (i == 8) break;
System.out.print(i + " ");
}
Output: 1 2 4 5 7
(3 and 6 are skipped by continue; at 8 the loop breaks.)

Caution with continue in a while loop: if the update comes after continue, it may be skipped and the loop may never end. As run:
int m = 1;
while (m <= 20)
{
m = m * 2;
if (m == 8) continue;
System.out.print(m + " ");
}
Output: 2 4 16 32 (8 is skipped; the update is before continue, so the loop is safe).

Use of loops for checking: prime test by counting factors: for (int i = 1; i <= n; i++) if (n % i == 0) factors++; n is prime if factors == 2. For 29: prime (as run).

Worked example

(2 marks) Distinguish between break and continue.

Try it first, then show the solutionSolution

1. break terminates the loop and control moves to the statement after it - 1 mark.
2. continue skips the remaining statements of the current iteration and starts the next iteration - 1 mark.

Answer: break ends the loop completely and passes control to the statement after the loop; continue skips only the rest of the current iteration and moves on to the next iteration of the same loop.

Iterative Statements in Java in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• break, continue, Digit Extraction and Series Programs Using Loops
• for, while and do-while Loops with Output Tracing and Loop Conversion

Iterative Statements in Java: syntax and key facts

for

for (init; condition; update) { body }

Entry-controlled; known count.

while / do-while

while (condition) { body; update; } do { body; update; } while (condition);

do-while runs at least once.

Digit loop

while (n > 0) { d = n % 10; ...; n = n / 10; }

Reverse: rev = rev * 10 + d.

Jump statements

break: leave loop; continue: next iteration

Both act on the innermost loop.

Infinite / delay

for (;;), while (true); delay: for (long t = 1; t <= N; t++);

Empty body = delay.

How the school exam asks Iterative Statements in Java

The question patterns to expect, and the method that works for each.

Tricks to remember Iterative Statements in Java

Short memory aids. Say each one aloud once, then use it on a question the same day.

• I-T-B-U

  Initialise, Test, Body, Update: the four parts of every loop.

  Use it when: Writing and converting loops.

• do-while = do then check

  The 'do' comes first, so the body runs before the check.

  Use it when: Exit control.

• %10 and /10

  % 10 picks the last digit; / 10 drops it.

  Use it when: Digit programs.

Iterative Statements in Java: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section B style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 7-mark question split into 2 + 3 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Iterative Statements in Java

The slips examiners see most often, and what to write instead.

• ✗Mistake: Off-by-one iteration counts

  < and <= confused.

  Wrong working

  for (i = 1; i < 10; i++) to print 1 to 10

  Right working

  for (i = 1; i <= 10; i++)

  ✓Do this: Check the first and last values in a trace.

  Usually costs: 1 to 2 marks.

• ✗Mistake: Losing the original number

  Dividing n itself in a digit loop.

  ✓Do this: Work on a copy so that n is available after the loop.

  Usually costs: 2 to 3 marks.

• ✗Mistake: Semicolon after the loop header

  Habit from statements.

  Wrong working

  for (i = 1; i <= 5; i++); System.out.println(i);

  Right working

  for (i = 1; i <= 5; i++) System.out.println(i);

  ✓Do this: No semicolon after for (...) or while (...) unless an empty body is intended.

  Usually costs: 1 to 2 marks.

• ✗Mistake: Missing semicolon after do-while

  Other loops do not need it.

  ✓Do this: do { ... } while (condition);

  Usually costs: 1 mark.

• ✗Mistake: Accumulator not initialised

  Declared without a value.

  ✓Do this: Start sums at 0 and products (factorial) at 1.

  Usually costs: 1 mark.

Practice questions on Iterative Statements in Java

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   Which statement skips the rest of the current iteration?
   (a) break
   (b) continue
   (c) exit
   (d) return

   Hint

   Next iteration.

   Answer

   (b) continue

2. Q2 · 1 mark · MCQExam level

   How many times does this loop execute? for (int i = 0; i < 20; i += 4)
   (a) 4
   (b) 5
   (c) 6
   (d) 20

   Hint

   0, 4, 8, ...

   Answer

   (b) 5 (i = 0, 4, 8, 12, 16)

3. Q3 · 2 marks · Very short answerHarder exam level

   Write a for loop to find the sum 1 + 1/2 + 1/3 + 1/4 + 1/5. What is the result?

   Hint

   1.0 / i.

   Answer

   double s = 0; for (int i = 1; i <= 5; i++) s = s + 1.0 / i; Result (as run): 2.283333333333333

4. Q4 · 2 marks · Very short answerExam level

   Convert into a do-while loop: int s = 0; for (int i = 2; i <= 20; i += 2) s += i;

   Hint

   Init, body, update, condition.

   Answer

   int s = 0, i = 2;
   do
   {
   s += i;
   i += 2;
   } while (i <= 20);
   (s = 110)

5. Q5 · 2 marks · Short answerHOTS / competency

   Give the output:
   int m = 1;
   while (m <= 20)
   {
   m = m * 2;
   if (m == 8) continue;
   System.out.print(m + " ");
   }

   Hint

   m is doubled before the test.

   Answer

   2 4 16 32

6. Q6 · 2 marks · Very short answerHarder exam level

   What is a delay loop? Why is its delay not exact?

   Hint

   Empty body.

   Answer

   A loop with an empty body that only counts, used to pause a program (for (long t = 1; t <= N; t++);). Its delay depends on the speed of the computer, so the same loop takes different times on different machines.

7. Q7 · 15 marks · Long answerHarder exam level

   Write a program to check whether a number is an Armstrong number (equal to the sum of the cubes of its digits, for a three-digit number). Test with 153.

   Hint

   Digit loop with d * d * d.

   Answer

   import java.util.*;
   class Armstrong
   {
   public static void main(String args[])
   {
   Scanner sc = new Scanner(System.in);
   System.out.print("Enter a three-digit number: ");
   int num = sc.nextInt();
   int t = num, arm = 0;
   while (t > 0)
   {
   int d = t % 10;
   arm += d * d * d;
   t /= 10;
   }
   if (arm == num)
   System.out.println(num + " is Armstrong");
   else
   System.out.println(num + " is not Armstrong");
   }
   }
   Sample run (as run, input 153): 153 is Armstrong (1 + 125 + 27 = 153).

8. Q8 · 2 marks · Very short answerHarder exam level

   Write a loop to count the factors of n and decide whether n is prime. What is printed for n = 29?

   Hint

   Prime has exactly two factors.

   Answer

   int factors = 0; for (int i = 1; i <= n; i++) if (n % i == 0) factors++; System.out.println(n + (factors == 2 ? " is prime" : " is not prime")); Output: 29 is prime

9. Q9 · 3 marks · Short answerHOTS / competency

   The prime-checking loop above tests every number up to n. Suggest two ways to make it faster and explain why each is correct.

   Hint

   break; stop early.

   Answer

   (1) Test divisors only from 2 to n / 2 (no factor other than n itself is larger than n / 2), and decide prime if none divides n. (2) Use break as soon as a divisor is found, since one divisor is enough to show n is not prime. Both give the same answer with fewer iterations.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Which loops are entry-controlled?Show answer

   for and while.

2. 2.Minimum number of times a do-while body runs?Show answer

   Once.

3. 3.Value of 6! ?Show answer

   720

4. 4.Write an infinite for loop.Show answer

   for (;;) { }

5. 5.What does continue do in a for loop?Show answer

   Skips to the update and the next test.

6. 6.Expression to remove the last digit of n?Show answer

   n = n / 10

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Loop parts: initialise, test, body, update.
• ☐Entry-controlled: for, while (may run 0 times); exit-controlled: do-while (at least once).
• ☐for when count is known; while when it is not; do-while when the body must run first.
• ☐Multiple counters: for (i = 1, j = 10; i < j; i++, j--).
• ☐Infinite: for (;;), while (true); delay: empty-body loop.
• ☐break leaves the loop; continue goes to the next iteration.

Iterative Statements in Java: frequently asked questions