break, continue, Digit Extraction and Series Programs in Java (ICSE Class 9)

Understand break, continue, Digit Extraction and Series Programs Using Loops

break, continue, Digit Extraction and Series Programs Using Loops: key facts

Digit operations

• •last digit: n % 10
• •drop the last digit: n / 10
• •loop while n > 0

Integer division is needed.

Reverse

• •rev = rev times 10 + n % 10
• •start rev = 0
• •keep the original in t

Compare rev with t for a palindrome.

Accumulators

• •sum starts at 0
• •product starts at 1
• •factorial f = f times i

Use long for large factorials.

Jumps

break: leave the loop | continue: skip to the next pass

Only the nearest loop is affected.

How to answer break, continue, Digit Extraction and Series Programs Using Loops questions

1. 1Save the original number if it is needed later.
2. 2Set the accumulators (sum, count, reverse) to their starting values.
3. 3Loop while n > 0: take d = n % 10, update the accumulators, set n = n / 10.
4. 4After the loop, use the results; compare with the saved number for palindrome or Armstrong checks.

break, continue, Digit Extraction and Series Programs Using Loops in real life

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

Tricks to remember break, continue, Digit Extraction and Series Programs Using Loops

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

• Mod takes, div drops

  n % 10 takes the last digit and n / 10 drops it.

  Use it when: Digit programs.

• Break leaves, continue skips

  break leaves the loop; continue skips one pass.

  Use it when: Jump statements.

• Save before you destroy

  Copy n before a digit loop if you need it afterwards.

  Use it when: Palindromes.

break, continue, Digit Extraction and Series Programs Using Loops: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

for (int i = 0; i < 3; i++)
{
if (i == 1)
break;
System.out.print(i);
}

int n = 2706, s = 0;
while (n > 0)
{
s = s + n % 10;
n = n / 10;
}
System.out.println(s);

for (int i = 1; i <= 6; i++)
{
if (i == 4)
break;
if (i % 2 == 0)
continue;
System.out.print(i + " ");
}

int n = 1331, t = n, rev = 0;
while (n > 0)
{
rev = rev * 10 + n % 10;
n = n / 10;
}
if (rev == t)
System.out.println("Palindrome");
else
System.out.println("Not a palindrome");

long f = 1;
for (int i = 1; i <= 5; i++)
f = f * i;
System.out.println(f);

Where students lose marks in break, continue, Digit Extraction and Series Programs Using Loops

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

• ✗Mistake: Using the changed n in a comparison

  n is zero after the loop.

  Wrong working

  if (rev == n)

  Right working

  keep t = n and use if (rev == t)

  ✓Do this: Save the original.

  Usually costs: 2 marks

• ✗Mistake: Wrong starting value

  The product accumulator starts at 0.

  Wrong working

  long f = 0; f = f * i

  Right working

  long f = 1;

  ✓Do this: Product starts at 1, sum at 0.

  Usually costs: 1 mark

• ✗Mistake: continue before the update in a while loop

  The loop stays on the same value.

  Wrong working

  continue; placed before i++ in a while loop

  Right working

  Update first or use a for loop

  ✓Do this: Check the update.

  Usually costs: 2 marks

Practice questions on break, continue, Digit Extraction and Series Programs Using Loops

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 · MCQBoard level

   The statement that terminates the nearest loop immediately is:
   (a) continue (b) break (c) skip (d) stop

   Hint

   It is also used in switch.

   Answer

   (b) break

2. Q2 · 2 marks · Very short answerBoard level

   Write a loop that adds the even numbers from 2 to 20 and state the sum.

   Hint

   Step of 2.

   Answer

   int s = 0;
   for (int i = 2; i <= 20; i += 2)
   s += i;
   Sum = 2 + 4 + ... + 20 = 110

3. Q3 · 3 marks · Short answerHarder board level

   Write a loop to count the digits of n = 90210 and state the count.

   Hint

   Drop one digit per pass.

   Answer

   int n = 90210, c = 0;
   while (n != 0)
   {
   c++;
   n = n / 10;
   }
   The loop runs 5 times (90210, 9021, 902, 90, 9), so c = 5.

4. Q4 · 3 marks · Short answerHarder board level

   Find the output:

   for (int i = 1; i <= 7; i++)
   {
   if (i % 3 == 0)
   continue;
   System.out.print(i + " ");
   }

   Hint

   Skip multiples of 3.

   Answer

   1 2 4 5 7

5. Q5 · 4 marks · Short answerHOTS / competency

   A number is perfect if the sum of its factors smaller than the number equals the number. Write a loop that finds this sum for n and show that 28 is perfect but 12 is not.

   Hint

   Test i from 1 to n / 2 with n % i == 0.

   Answer

   int s = 0;
   for (int i = 1; i <= n / 2; i++)
   {
   if (n % i == 0)
   s = s + i;
   }
   For 28: 1 + 2 + 4 + 7 + 14 = 28, so it is perfect. For 12: 1 + 2 + 3 + 4 + 6 = 16, which is not 12, so it is not perfect.

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 expression gives the last digit of n?Show answer

   n % 10

2. 2.Which expression removes the last digit?Show answer

   n / 10

3. 3.Starting value of a product accumulator?Show answer

   1

4. 4.Starting value of rev in a reverse program?Show answer

   0

5. 5.Which statement leaves the loop?Show answer

   break

6. 6.What is 5 factorial?Show answer

   120

break, continue, Digit Extraction and Series Programs Using Loops: frequently asked questions