Loops in Programming - JSS 2 note

LOOPS IN PROGRAMMING

Subject: Digital Technologies
Class: JSS 2
Term: Second Term
Week: 8
Topic: Loops in Programming
Duration: 80 Minutes (Double Period)

1. Learning Objectives

By the end of the lesson, students should be able to:

• Explain the meaning of a loop in programming.
• State the importance of loops in computer programs.
• Identify the FOR loop and WHILE loop.
• Explain how loops are used to repeat instructions.
• Use loop blocks in Scratch to create a simple repeating action.

2. Introduction

In everyday life, we sometimes repeat the same action several times. For example, a teacher may ask students to write a sentence ten times, or a person may count numbers from one to ten.

In programming, repeating the same instruction manually can make a program unnecessarily long. Programmers use loops to repeat instructions automatically. Loops are useful in games, animations, calculations and many other computer applications.

3. Meaning of a Loop

Definition: A loop is a programming structure that repeats a set of instructions either a specified number of times or while a particular condition is satisfied.

Loops help programmers avoid writing the same instructions repeatedly. Instead, a group of instructions can be placed inside a loop and executed multiple times.

Example Without a Loop

Suppose a sprite must move forward five times. Without a loop, the movement instruction may need to be repeated several times.

MOVE 10 STEPS MOVE 10 STEPS MOVE 10 STEPS MOVE 10 STEPS MOVE 10 STEPS

Example With a Loop

The same task can be completed more conveniently with a loop.

REPEAT 5 TIMES MOVE 10 STEPS

The loop repeats the movement instruction five times.

4. Importance of Loops

Loops are important in programming for the following reasons:

1. Reduce repetition: They prevent programmers from writing the same instruction many times.
2. Make programs shorter: A loop can replace many repeated instructions.
3. Save time: Instructions can be repeated automatically.
4. Improve readability: A well-designed loop makes the purpose of a program easier to understand.
5. Support animation and games: Loops can repeatedly move sprites, check conditions or update scores.
6. Perform repeated calculations: Programs can use loops to process many numbers or records.

5. Types of Loops

Two common types of loops are the FOR loop and the WHILE loop.

A. FOR Loop

Definition: A FOR loop is commonly used when the number of repetitions is known or controlled by a counter.

For example, a program may need to display a message five times or count from one to ten.

FOR count FROM 1 TO 5 DISPLAY "Welcome" END FOR

This example displays “Welcome” five times, once for each count from 1 through 5.

Characteristics of a FOR Loop

• It is useful when the number of repetitions is known.
• It can use a counter to keep track of repetitions.
• It helps perform repeated tasks in an organised way.

B. WHILE Loop

Definition: A WHILE loop repeats a set of instructions as long as a specified condition remains true.

The condition is checked before each repetition. If the condition is false at the beginning, the instructions inside the loop may not execute at all.

SET count TO 1 WHILE count <= 5 DISPLAY count CHANGE count BY 1 END WHILE

This example displays the numbers 1, 2, 3, 4 and 5. The count increases after each repetition, and the loop stops when count becomes 6 because the condition is no longer true.

Characteristics of a WHILE Loop

• It depends on a condition.
• It continues while the condition is true.
• It is useful when the number of repetitions depends on changing circumstances.
• The condition and the instructions inside the loop must be designed carefully so the loop can stop when required.

6. Difference Between FOR and WHILE Loops

FOR Loop	WHILE Loop
Often used when the number of repetitions is known.	Often used when repetition depends on a condition.
Commonly uses a counter or a range of values.	Checks a condition before each repetition.
Example: Repeat an instruction five times.	Example: Continue while a score is below 100.
Usually stops when the specified repetitions are completed.	Stops when its condition becomes false, assuming the loop can reach that state.

Important: A WHILE loop may continue indefinitely if its condition never becomes false. Programmers should make sure the loop has a suitable stopping condition or another way to end it.

7. Loops in Scratch

Scratch is a block-based programming environment. Its Control category contains loop blocks that allow instructions to be repeated.

Common Loop Blocks in Scratch

Scratch Block	Function
repeat (10)	Repeats the instructions inside the block a specified number of times.
forever	Repeats the instructions continuously until the script is stopped.
repeat until (condition)	Repeats the instructions until the specified condition becomes true.

These blocks make it easier for beginners to understand repetition without having to type programming instructions.

8. Practical Activity: Moving a Sprite Repeatedly

In this activity, students will use Scratch to make a sprite move repeatedly.

Steps

1. Open Scratch and create a new project.
2. Select a sprite and open the Events category.
3. Add the when green flag clicked block.
4. Open the Control category and add a repeat (5) block beneath the event block.
5. Place a move 10 steps block inside the repeat block.
6. Add a wait 1 seconds block inside the repeat block so that the movement can be observed clearly.
7. Click the green flag to run the program.
8. Observe the sprite as it moves five times.

Program Structure

WHEN GREEN FLAG CLICKED REPEAT 5 TIMES MOVE 10 STEPS WAIT 1 SECOND

The program moves the sprite ten steps and waits one second during each repetition. It repeats these actions five times and then stops the loop.

9. Practical Activity: Using a Condition to Repeat

Students can also explore the repeat until block.

1. Start a new Scratch script with the green flag event.
2. Add a repeat until block from the Control category.
3. Use a suitable sensing condition, such as touching the edge, if available in the chosen project.
4. Place a movement block inside the repeat-until block.
5. Run the program and observe how the movement continues until the condition is satisfied.

Learning point: The repeat block stops after the specified number of repetitions. The repeat-until block stops when its condition becomes true.

10. Applications of Loops

Application	How a Loop Is Used
Computer games	Repeatedly updates movement, checks game events or monitors scores.
Animations	Repeats actions to create continuous movement or visual effects.
Counting programs	Displays or processes a sequence of numbers.
Quiz applications	Processes questions or repeatedly checks a player's responses.
Data processing	Performs similar operations on many records or items.

11. Summary

A loop is a programming structure that repeats instructions. Loops reduce repetition, make programs shorter and help automate tasks.

A FOR loop is commonly used when the number of repetitions is known, while a WHILE loop repeats as long as its condition remains true. In Scratch, the repeat, forever and repeat-until blocks are used to repeat instructions. Programmers must ensure that condition-based loops can stop when required.

12. Evaluation Questions

1. What is a loop in programming?
2. State four advantages of using loops.
3. Explain the meaning of a FOR loop.
4. Explain the meaning of a WHILE loop.
5. State three differences between FOR and WHILE loops.
6. Name three loop blocks available in Scratch.
7. Describe how to make a sprite move five times using a Scratch loop.
8. Why should programmers avoid an unintended infinite loop?

13. Assignment

1. Define a loop in programming.
2. Explain three reasons loops are useful.
3. Differentiate between a FOR loop and a WHILE loop.
4. Write pseudocode that displays “Good morning” five times using a FOR loop.
5. Describe a Scratch program that uses a repeat block to make a sprite move ten steps five times.

14. Interactive Quiz

Select one answer for each question and click Submit Quiz to check your score.

1. What is a loop in programming?

A device used to print documents A structure that repeats instructions A type of computer monitor A method of shutting down a computer

2. Which is an important advantage of loops?

They prevent all calculations They remove the need for instructions They make every program run forever They reduce repeated instructions

3. Which loop is commonly used when the number of repetitions is known?

FOR loop WHILE loop only IF statement ELSE statement

4. A WHILE loop continues repeating while what is true?

The monitor is switched on The printer has paper Its condition remains true The keyboard is connected

5. Which Scratch block repeats instructions a specified number of times?

If Repeat Say Wait only

6. Which Scratch block repeats instructions continuously until the script is stopped?

Repeat (5) If-else Set variable Forever

7. What happens when a repeat (5) loop completes all five repetitions?

The loop finishes its repetitions The computer must shut down The loop automatically repeats forever The Scratch project is deleted

8. What is an infinite loop?

A loop that runs exactly twice A loop that contains no instructions A loop that continues without reaching its intended stopping point A loop that always runs once

9. Which Scratch block repeats instructions until a specified condition becomes true?

Move 10 steps Repeat until Set Score to 0 When green flag clicked

10. Which of these is a practical application of loops?

Physically cleaning a keyboard Replacing a broken monitor Connecting a power cable Repeating sprite movements in an animation