Algorithms and Flowcharts ICSE Class 8: Characteristics, Symbols and Problems with Decision Making

What Algorithms and Flowcharts is about

Weightage: CISCE publishes no question paper, marking scheme or chapter weightage for Class VIII Computer Studies: your school sets and marks the exam. Algorithms and Flowcharts sits in the Theme: Algorithms and Flowcharts theme of the CISCE Curriculum for Upper Primary Classes (VI-VIII).Source: CISCE Curriculum for Upper Primary Classes (VI-VIII), RDCD 2016

Key concepts

Algorithm: definition and use

An algorithm is a finite sequence of clear, step-by-step instructions for solving a particular problem or doing a task.

Uses:

• It helps us think through a problem before writing a program.
• It is written in simple language, so anyone can follow and check it.
• It is independent of any programming language: the same algorithm can be coded in Java, Python or any other language.
• Errors in logic are easier to find and correct at this stage.

Example: area and perimeter of a rectangle
1. Start.
2. Input length L and breadth B.
3. Area = L × B.
4. Perimeter = 2 × (L + B).
5. Print Area and Perimeter.
6. Stop.

With L = 12 and B = 5, the algorithm prints Area = 60 and Perimeter = 34.

Worked example

Write an algorithm to find the simple interest and amount for principal P, rate R% and time T years. Trace it for P = 5000, R = 8, T = 3.

Try it first, then show the solutionSolution

1. 1. Start. 2. Input P, R, T. 3. SI = P × R × T ÷ 100. 4. Amount = P + SI. 5. Print SI and Amount. 6. Stop.
2. Trace: SI = 5000 × 8 × 3 ÷ 100 = 1200; Amount = 5000 + 1200 = 6200.

Answer: SI = 1200, Amount = 6200

Characteristics of a good algorithm

Characteristic	Meaning
Input	takes zero or more values from outside
Output	produces at least one result
Definiteness	every step is clear and unambiguous: it means exactly one thing
Finiteness	it ends after a limited number of steps
Effectiveness	every step is simple and can actually be carried out
Language independence	it can be turned into any programming language

A bad step: 'Add some sugar.' (How much? Not definite.)
A good step: 'Add 2 teaspoons of sugar.'

A set of steps that never stops (for example, 'Go back to step 1' with no way out) breaks finiteness, so it is not an algorithm.

Worked example

Which characteristic is missing in each? (i) 'Divide the bill among the friends and pay a fair amount.' (ii) A set of steps with no output.

Try it first, then show the solutionSolution

1. (i) 'A fair amount' is vague, so definiteness is missing.
2. (ii) An algorithm must produce at least one output, so output is missing.

Answer: (i) Definiteness (ii) Output

Steps to develop an algorithm

1. Understand the problem: read it carefully and know what is asked.
2. Identify the input: what data are given?
3. Identify the output: what result is wanted?
4. Plan the process: the formula or decisions needed to get from input to output.
5. Write the steps in order, starting with Start and ending with Stop.
6. Test (dry run) the algorithm with sample data, including boundary values (for example, exactly 40 marks for a pass mark of 40), and correct any errors.

Example: 'Find whether a student has passed if the pass mark is 40.'

• Input: marks M. Output: 'Pass' or 'Fail'.
• Process: decide whether M ≥ 40.
• Test with M = 40 (Pass) and M = 39 (Fail).

Worked example

For the problem 'convert a temperature from Celsius to Fahrenheit', state the input, output and process, and test with 35 °C.

Try it first, then show the solutionSolution

1. Input: Celsius C. Output: Fahrenheit F. Process: F = C × 9 ÷ 5 + 32.
2. Test: F = 35 × 9 ÷ 5 + 32 = 63 + 32 = 95.

Answer: 95 °F

Flowchart and its symbols

A flowchart is a diagram of an algorithm, in which each kind of step is drawn as a standard symbol and the symbols are joined by arrows that show the order of steps.

Symbol	Shape	Used for
Terminal	oval (rounded rectangle)	Start and Stop
Input/Output	parallelogram	Input (read) or Output (print, display)
Process	rectangle	calculations and assignments, such as Area = L × B
Decision	diamond (rhombus)	a question with Yes/No (True/False) answers; two exits
Flow line	arrow	direction of flow
Connector	small circle	joins parts of a flowchart, for example across pages

Rules for drawing:

• Exactly one Start and at least one Stop.
• Flow normally goes top to bottom or left to right.
• A decision box has one entry and two labelled exits (Yes and No).
• Arrows must not cross where avoidable; every path must reach Stop.
• Write short, clear text in each box.

Worked example

Name the flowchart symbol for (i) Print 'Pass' (ii) Is M ≥ 40? (iii) SI = P × R × T ÷ 100 (iv) Stop.

Try it first, then show the solutionSolution

1. (i) Output: parallelogram. (ii) Decision: diamond.
2. (iii) Process: rectangle. (iv) Terminal: oval.

Answer: Parallelogram; diamond; rectangle; oval

Decision making: one and two conditions

A decision step asks a question whose answer is Yes or No, and the algorithm follows a different path for each.

Greater of two numbers
1. Start.
2. Input A, B.
3. If A > B then print A, else print B.
4. Stop.
Flowchart: Start → [Input A, B] → ◇ A > B? → Yes: [Print A] / No: [Print B] → Stop.
Trace: A = 17, B = 29 → 17 > 29 is No → prints 29.

Odd or even
1. Start. 2. Input N. 3. If N % 2 = 0 (remainder 0 when divided by 2) then print 'Even', else print 'Odd'. 4. Stop.
Trace: N = 27 → remainder 1 → Odd.

Positive, negative or zero (two decisions)
1. Start. 2. Input N.
3. If N > 0, print 'Positive'.
4. Else, if N < 0, print 'Negative'.
5. Else print 'Zero'.
6. Stop.
Trace: N = −7 → not > 0, is < 0 → Negative.

Worked example

In the 'greater of two numbers' algorithm, what is printed when A = 8 and B = 8? Is that acceptable?

Try it first, then show the solutionSolution

1. 8 > 8 is false (No), so the else branch prints B, which is 8.
2. Since both are equal, printing 8 is correct; a better algorithm could add a check to print 'Both are equal'.

Answer: 8; correct, though an 'equal' message would be clearer.

Decisions inside decisions

Some problems need several decisions one after another (a chain) or one inside another (nested).

Largest of three numbers A, B, C (nested)
1. Start. 2. Input A, B, C.
3. If A > B then

• if A > C, print A, else print C.

4. Else

• if B > C, print B, else print C.

5. Stop.
Trace: A = 15, B = 25, C = 20 → A > B? No → B > C? Yes → prints 25.

Grade from marks (chain of decisions)
1. Start. 2. Input M.
3. If M ≥ 90, grade = 'A'; else if M ≥ 75, grade = 'B'; else if M ≥ 60, grade = 'C'; else grade = 'D'.
4. Print grade. 5. Stop.
Trace: M = 82 → not ≥ 90, is ≥ 75 → B. Check boundaries: 90 → A, 60 → C, 59 → D.

Leap year (year Y)

• If Y is divisible by 400 → leap year;
• else if Y is divisible by 100 → not a leap year;
• else if Y is divisible by 4 → leap year;
• else → not a leap year.

Traces: 2024 → leap; 1900 → not leap; 2000 → leap; 2023 → not leap.

Worked example

Trace the 'largest of three' algorithm for A = 30, B = 10, C = 45, showing each decision.

Try it first, then show the solutionSolution

1. A > B? 30 > 10: Yes. Then A > C? 30 > 45: No.
2. So print C = 45.

Answer: 45

Algorithms and Flowcharts 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

• Decision Making in Algorithms and Flowcharts
• A Good Algorithm, Its Development Steps and Flowchart Symbols

Algorithms and Flowcharts: syntax and key facts

Shape of every algorithm

1. 1.Input
2. 2.Process
3. 3.Output

Start first, Stop last.

Characteristics

Input, Output, Definiteness, Finiteness, Effectiveness

Plus language independence.

Flowchart symbols

Oval: Start/Stop; Parallelogram: Input/Output; Rectangle: Process; Diamond: Decision; Arrow: flow; Circle: connector

Decision has two labelled exits.

Even test

N % 2 = 0 → Even, otherwise Odd

% gives the remainder.

Decision pattern

If condition then step A, else step B

Exactly one branch runs.

Algorithms and Flowcharts: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Algorithms and Flowcharts

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

Tricks to remember Algorithms and Flowcharts

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

• IODFE: 'I Owe Dad Five Eggs'

  Input, Output, Definiteness, Finiteness, Effectiveness.

  Use it when: Characteristics of a good algorithm.

• Shapes by job

  Oval = open and close (Start/Stop); Parallelogram = pass data in or out; Rectangle = work; Diamond = decide.

  Use it when: Flowchart symbols.

• Diamond has two doors

  Every decision diamond must have two labelled exits: Yes and No.

  Use it when: Drawing decision boxes.

• Test the edge

  Always try the boundary value (40 for a pass mark of 40).

  Use it when: Dry runs.

Algorithms and Flowcharts: 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 6-mark question split into 2 + 2 + 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 Algorithms and Flowcharts

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

• ✗Mistake: Leaving out Start or Stop

  Every algorithm and flowchart must begin with Start and end with Stop.

  ✓Do this: Write them first, then fill the middle.

  Usually costs: 1 mark.

• ✗Mistake: Unlabelled decision exits

  The examiner cannot tell which path is Yes and which is No.

  ✓Do this: Label both arrows from every diamond.

  Usually costs: 1 mark.

• ✗Mistake: Wrong symbol for a step

  Calculations go in rectangles; input and output in parallelograms.

  Wrong working

  Rectangle for 'Input A, B'

  Right working

  Parallelogram for 'Input A, B'

  ✓Do this: Ask: am I reading/printing (parallelogram) or calculating (rectangle)?

  Usually costs: 1 mark per symbol.

• ✗Mistake: Using > when the condition says 'or more'

  The boundary value is then handled wrongly.

  ✓Do this: '40 or more' means ≥ 40.

  Usually costs: 1 mark.

• ✗Mistake: Using loops

  The Class VIII curriculum stops at decision making; loops are excluded.

  ✓Do this: Solve with sequence and decisions only.

  Usually costs: Answers may not match the expected method.

Practice questions on Algorithms and Flowcharts

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

   The flowchart symbol for a calculation is the:
   (a) oval
   (b) rectangle
   (c) diamond
   (d) parallelogram

   Hint

   Process.

   Answer

   (b)

2. Q2 · 1 mark · Very short answerExam level

   Which characteristic means every step must have only one meaning?

   Hint

   Clear.

   Answer

   Definiteness.

3. Q3 · 2 marks · Short answerExam level

   Write an algorithm to find the area and perimeter of a rectangle.

   Hint

   L × B; 2(L + B).

   Answer

   1. Start. 2. Input L, B. 3. Area = L × B. 4. Perimeter = 2 × (L + B). 5. Print Area, Perimeter. 6. Stop.

4. Q4 · 2 marks · Short answerExam level

   State the use of the connector symbol and the flow line.

   Hint

   Joining; direction.

   Answer

   The connector (small circle) joins different parts of a flowchart, for example across pages; flow lines (arrows) show the direction of flow from one step to the next.

5. Q5 · 1 mark · Assertion-reasonHarder exam level

   Assertion (A): A set of instructions that never ends is not an algorithm.
   Reason (R): An algorithm must have finiteness.
   (a) (A) is true and (R) is false.
   (b) (A) is false and (R) is true.
   (c) Both (A) and (R) are true, and (R) is the correct explanation for (A).
   (d) Both (A) and (R) are true, but (R) is not the correct explanation for (A).

   Hint

   It must stop.

   Answer

   (c)

6. Q6 · 2 marks · Short answerHarder exam level

   Write an algorithm to convert Celsius to Fahrenheit and find the output for 100 °C.

   Hint

   F = C × 9/5 + 32.

   Answer

   Start; input C; F = C × 9 ÷ 5 + 32; print F; Stop. For 100 °C: 180 + 32 = 212 °F.

7. Q7 · 3 marks · Short answerHarder exam level

   Write an algorithm to print whether a number is positive, negative or zero. Trace for −7 and 0.

   Hint

   Two decisions.

   Answer

   Start; input N; if N > 0 print 'Positive', else if N < 0 print 'Negative', else print 'Zero'; Stop. −7 → Negative; 0 → Zero.

8. Q8 · 3 marks · Short answerHarder exam level

   Draw a flowchart to input age and print 'Can vote' if age is 18 or more, otherwise 'Cannot vote'. What is printed for 17?

   Hint

   Diamond with ≥.

   Answer

   Start (oval) → Input age (parallelogram) → diamond 'age ≥ 18?' → Yes: Print 'Can vote'; No: Print 'Cannot vote' (parallelograms) → Stop (oval). For 17: Cannot vote.

9. Q9 · 3 marks · Short answerHarder exam level

   List the six steps to develop an algorithm.

   Hint

   Understand to test.

   Answer

   Understand the problem; identify input; identify output; plan the process; write the steps in order; test with sample data and correct errors.

10. Q10 · 2 marks · Short answerHarder exam level

    The steps to swap two numbers are: T = A; A = B; B = T. Dry run with A = 4, B = 9 and give the final values. Why is T needed?

    Hint

    Write values after each step.

    Answer

    After T = A: T = 4. After A = B: A = 9. After B = T: B = 4. Final A = 9, B = 4. T keeps the old value of A, which would otherwise be lost when A = B runs.

11. Q11 · 3 marks · Short answerHOTS / competency

    Write an algorithm to find whether three lengths can form a triangle (each pair of sides must add to more than the third). Test with (3, 4, 8) and (5, 6, 7).

    Hint

    Three conditions joined by AND.

    Answer

    Start; input a, b, c; if a + b > c and a + c > b and b + c > a then print 'Triangle possible' else print 'Not possible'; Stop. (3, 4, 8): 3 + 4 = 7 is not > 8 → Not possible. (5, 6, 7): all true → Triangle possible.

12. Q12 · 3 marks · Short answerHOTS / competency

    A student's flowchart for 'greater of two numbers' prints A whenever A ≥ B and B otherwise. Another student says it gives a wrong answer when the numbers are equal. Who is right? Suggest an improvement.

    Hint

    What is the 'greater' of 8 and 8?

    Answer

    The flowchart is not wrong: for equal numbers it prints A, which equals the greater value. But it does not tell the user that they are equal. Improvement: add a first decision 'A = B?' → Yes: print 'Both are equal'; No: continue with 'A > B?'.

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.Define algorithm.Show answer

   A finite sequence of clear, step-by-step instructions to solve a problem.

2. 2.Define flowchart.Show answer

   A diagram of an algorithm using standard symbols joined by arrows.

3. 3.Symbol for Start/Stop?Show answer

   Oval (terminal).

4. 4.Symbol for input/output?Show answer

   Parallelogram.

5. 5.What does finiteness mean?Show answer

   The algorithm ends after a limited number of steps.

6. 6.How many exits does a decision box have?Show answer

   Two (Yes and No).

7. 7.What does N % 2 give?Show answer

   The remainder when N is divided by 2.

Quick revision checklist

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

• ☐Can you define algorithm and flowchart?
• ☐Can you list five characteristics of a good algorithm?
• ☐Can you draw all six symbols and name their uses?
• ☐Can you write an algorithm for odd/even and for the greater of two numbers?
• ☐Can you draw a flowchart with a decision?
• ☐Can you dry run an algorithm with given values?

Algorithms and Flowcharts: frequently asked questions