In visual programming languages like Scratch, the foundation of any program is built upon core programming constructs that determine how instructions are executed. These constructs—sequences, variables, loops, and conditionals—form the building blocks for creating interactive programs, games, and animations. Understanding how to use these constructs effectively is crucial for developing logical thinking and problem-solving skills in programming.

1. Sequence: The Order of Execution

A sequence in programming refers to a set of instructions that are executed one after the other in a specific order. Just like following steps in a recipe, computers follow instructions in the order they appear.

Example of Sequence in Scratch:

Imagine you want a sprite (a character in Scratch) to move forward, say “Hello!”, and then change color. The correct sequence of blocks would be:

1. Move 10 steps forward
2. Say “Hello!” for 2 seconds
3. Change color effect by 25

If the order of the blocks was different (e.g., changing color before moving), the program would behave differently. Sequence ensures the correct flow of actions.

Real-World Analogy:

Think of a morning routine:

1. Wake up
2. Brush your teeth
3. Eat breakfast
4. Go to school

If the order changes (e.g., eating before brushing teeth), the outcome is different. Similarly, in programming, the order of instructions impacts the program’s behavior.

2. Variables: Storing and Managing Data

A variable is a storage location in a program that holds data that can change while the program is running. In Scratch, variables can store numbers, text, or other values that influence the program’s behavior.

How to Use Variables in Scratch:

1. Creating a variable: Click the “Make a Variable” button in the Variables category.
2. Assigning values: You can set a variable to store numbers or words (e.g., “score = 0”).
3. Changing values: The value of a variable can be updated as the program runs (e.g., increasing score in a game).

Example of Variables in a Scratch Game:

• A score variable can be used to keep track of a player’s score in a game.
• A timer variable can be used to count how long a player has been playing.

Example Scratch Code for a Score System:

 

When green flag clicked

   Set [score] to 0

   Forever

      If < touching [coin] > then

         Change [score] by 1

      End

 

In this example, every time the sprite touches a coin, the score variable increases by 1.

Real-World Analogy:

Think of a piggy bank. If you start with $0 and keep adding coins, the total amount changes dynamically. Similarly, variables store and update values throughout the program.

3. Loops: Repeating Actions (Iteration)

Loops allow programmers to repeat a set of instructions multiple times, making programs more efficient and avoiding redundant code.

Types of Loops in Scratch:

1. Repeat Loop (Fixed Repetition) – Runs a set of instructions a specific number of times.
   • Example: “Repeat 10” moves a sprite 10 steps forward 10 times.
2. Forever Loop (Infinite Repetition) – Repeats the instructions endlessly until stopped.
   • Example: “Forever” makes a character keep running until the program stops.
3. Repeat Until Loop (Conditional Repetition) – Repeats until a condition is met.
   • Example: “Repeat until score = 10” will keep looping until the score reaches 10.

Example Scratch Code for Loops:

 

When green flag clicked

   Repeat (5)

      Move 10 steps

      Wait 1 second

   End

 

In this example, the sprite will move forward 10 steps, pause, and repeat this action 5 times.

Real-World Analogy:

• Repeat Loop: Writing “I will do my homework” 10 times as a school punishment.
• Forever Loop: A fan that keeps rotating as long as it’s turned on.
• Repeat Until Loop: Playing a game until you reach a target score.

4. Conditionals: Making Decisions in a Program

Conditionals allow a program to make decisions based on certain conditions. This makes programs interactive by responding to different situations.

Types of Conditional Statements in Scratch:

1. If-Then: Executes a block of code only if a condition is true.
   • Example: If a sprite touches the edge, it should bounce back.
2. If-Then-Else: Executes one block of code if a condition is true and another block if it is false.
   • Example: If the score is greater than 10, display “You win!” Else, continue the game.

Example Scratch Code for Conditionals:

 

When green flag clicked

   Forever

      If < touching [edge] > then

         Turn 180 degrees

      End

 

In this example, the sprite will turn around whenever it touches the screen’s edge.

Real-World Analogy:

• If-Then: If it rains, then take an umbrella.
• If-Then-Else: If you pass the exam, then celebrate; else, study harder.

5. Integration: Combining Constructs to Create Programs

To create fully functional programs, programmers integrate sequences, variables, loops, and conditionals to produce meaningful interactions.

Example of a Simple Game Using All Constructs:

A game where:

1. A sprite moves across the screen (sequence).
2. The player earns points by collecting coins (variables).
3. The game runs until the player reaches 10 points (loop).
4. If the player touches an obstacle, they lose (conditionals).

Scratch Code Example:

 

When green flag clicked

   Set [score] to 0

   Repeat until <(score) = 10>

      Move 5 steps

      If < touching [obstacle] > then

         Say “Game Over!”

         Stop all

      End

      If < touching [coin] > then

         Change [score] by 1

      End

   End

 

This game integrates all four constructs to make an interactive experience.

Why These Constructs Matter

• They simplify programming by breaking it into logical steps.
• They reduce redundancy and make code more efficient.
• They allow for problem-solving and encourage structured thinking.
• They prepare students for text-based programming by building a strong foundation in logical thinking.

By mastering sequences, variables, loops, and conditionals, students develop the core skills necessary to write more complex programs in future text-based languages like Python.

Final Thoughts

This section introduces students to the basic building blocks of programming in a visual language like Scratch. By understanding how sequences, variables, loops, and conditionals work together, students can build interactive projects, animations, and games. Mastering these concepts will prepare them for more advanced programming concepts in later years, ensuring they are ready for text-based languages like Python in Year 8.

This is Chapter 8.2: Basic Constructs, structured for Year 7 students in a way that engages them with practical examples and real-world applications. This prepares them for both creative projects in Scratch and future text-based programming languages like Python.