BBP Lesson 4: Conditionals and Decision Making

:dart: Learning Objectives

By the end of this lesson, you'll be able to:

• Understand how programs make decisions using if, elif, and else blocks
• Create conditional statements to control program flow
• Build nested conditionals for complex decision-making
• Connect visual blocks to real Python conditional syntax
• Debug common conditional logic errors

Definition: Conditionals are programming structures that compare values and execute different code paths based on whether conditions evaluate to True or False.

• Enable programs to make decisions based on data
• Control program flow through logical comparisons
• Foundation for interactive and responsive applications
• Essential for creating dynamic program behavior

Let's Get Started! :rocket:

Understanding Conditionals

The Logic of Decision Making

Purpose: Allow programs to respond differently based on varying conditions and user input.

In programming, conditionals enable decision-making by asking "if something is true", then proceeding with one task, "else" proceeding with another task. This fundamental concept allows programs to adapt their behavior based on different scenarios.

:information_source: Remember! Conditionals are like making choices in real life! Just like deciding "If it's raining, I'll take an umbrella, else I'll wear sunglasses," programs use the same logic to make decisions.

To use conditionals in EduBlocks:

1. Look for the Logic category in the left sidebar
2. Drag the if, elif, or else blocks you need
3. Drop them into your workspace

:bulb: Pro Tip

The Logic category is where all your decision-making blocks live. Get familiar with this section - you'll use it a lot!

The If Statement

Basic Conditional Execution

Purpose: Execute code blocks only when specified conditions are true.

Key Characteristics:

• C-shaped design allows nesting blocks inside
• Blocks nested inside run only if the statement is true
• Blocks outside remain unaffected by the condition
• Forms the foundation of conditional logic

The if statement represents the most basic form of conditional programming, enabling selective code execution based on boolean evaluations.

:information_source: Python Connection In text-based Python, an if statement looks like this:

if condition:
    # code to run if true

The EduBlocks if block works exactly the same way - it just looks more visual!

How to Use the If Block:

1. Drag the if block from the Logic category
2. Add a condition (like a comparison) to the diamond-shaped slot
3. Place the blocks you want to run inside the C-shape
4. Run your program to see it make decisions!

:bulb: Troubleshooting

If your if block isn't working:

• Check that you have a condition in the diamond slot
• Make sure your blocks are properly nested inside the C-shape
• Test with simple conditions first (like 5 > 3) to verify it works

The Elif Statement

Additional Conditional Paths

Purpose: Provide alternative conditions to check when the initial if statement is false.

Understanding Elif:

• Short form combining "else" and "if"
• Functions similarly to if blocks with conditional requirements
• Only runs if the above if block statement is False
• Must follow an if block in the conditional chain

:information_source: Remember! "Elif" = "Else If" - It's like saying "If the first thing isn't true, then check if this other thing is true."

How to Use the Elif Block:

1. Start with an if block first (elif can't go first!)
2. Drag the elif block directly below your if block
3. Add a new condition to check
4. Place code inside that runs when this condition is true

Elif Usage Example:

Input	Output

:bulb: Troubleshooting

Common elif mistakes:

• Putting elif before an if block (won't work!)
• Forgetting to add a condition to the elif
• Having gaps between your if and elif blocks

The Else Statement

Default Execution Path

Purpose: Provide a fallback action when all previous conditions are false.

Else Block Rules:

• Must follow an if block or elif block
• Cannot follow another else block
• Serves as the final block in conditional chains
• Runs only when all previous conditions are false

:information_source: Remember! The else block is like a safety net - it catches everything that didn't match your if or elif conditions. Think of it as "If none of the above are true, then do this instead."

How to Use the Else Block:

1. Start with an if block (and optionally elif blocks)
2. Drag the else block as the last block in your chain
3. Place code inside that runs when all other conditions are false
4. Note: else doesn't need a condition - it runs automatically!

Basic If...Else Example:

Input	Output

Extended If...Else Example:

Input	Output

Alternative If...Else Implementation:

Input	Output

:bulb: Pro Tip

Always consider adding an else block to handle unexpected cases. It's good practice to have a default action when none of your specific conditions match!

Understanding Conditional Flow

Sequential Evaluation Logic

Purpose: Understand how conditional statements are evaluated and why order matters.

Important Rule: When a conditional statement evaluates to true, it ignores subsequent conditional command blocks due to the "else" nature of elif and else blocks.

:information_source: Python Connection In Python, conditions are checked from top to bottom. Once a condition is True, Python runs that block and skips the rest. This is exactly how EduBlocks works too!

if score >= 90:
    print("A")  # If this runs...
elif score >= 80:
    print("B")  # ...this is skipped
else:
    print("C")  # ...and this too

Common Flow Mistakes:

Incorrect Flow Example:

:x: Input	Output

Correct Flow Example:

:white_check_mark: Input	Output

:bulb: Debugging Tip

If your conditionals aren't working as expected:

1. Check the order of your conditions
2. Make sure more specific conditions come before general ones
3. Use print blocks to see which path your program is taking
4. Remember: only ONE block in an if-elif-else chain will run!

Nesting Conditionals

Complex Decision Trees

Purpose: Create sophisticated decision-making structures by placing conditional blocks inside other conditional blocks.

Nested conditionals enable multi-level decision making, allowing programs to handle complex scenarios with multiple layers of conditions.

:information_source: Remember! Nesting is like having decisions within decisions. For example: "If it's the weekend, then if it's sunny, go to the park, else watch a movie."

How to Create Nested Conditionals:

1. Start with your outer if block
2. Inside that if block, drag another if block
3. Add conditions to both the outer and inner blocks
4. Keep track of your indentation levels
5. Test each level separately to debug

Nested Conditionals Example:

Input	Output

:bulb: Advanced Challenge

Try creating a simple game that uses nested conditionals! For example:

• Ask the user their age
• If they're over 10:
  • Ask their favorite color
  • If it's blue, print "Cool choice!"
  • Else print "Nice color!"
• Else tell them they're too young

This helps you practice multiple levels of decision-making!

Demo Project Example

Comprehensive Conditional Implementation

Purpose: Demonstrate practical application of conditionals combined with comparison and logical operators.

This example showcases how conditionals work together with various operators to create functional, interactive programs.

Complete Demo Project:

Input	Output

:rocket: Remix this! Check out the complete demo project at: https://project.edublocks.org/iR1i

Try These Modifications:

1. Change the conditions to check different values
2. Add more elif blocks for additional options
3. Nest an if statement inside one of the blocks
4. Add print statements to trace the program flow

:bulb: Professional Tip

Master conditional flow by understanding that conditions are evaluated sequentially from top to bottom. Once a condition is met, subsequent elif and else blocks are skipped. This behavior is crucial for creating efficient and predictable program logic.

Optional Challenges for Advanced Students :star2:

Challenge One: Grade Calculator

Create a program that:

1. Asks for a test score (0-100)
2. Uses if-elif-else to assign letter grades:
   • A: 90-100
   • B: 80-89
   • C: 70-79
   • D: 60-69
   • F: Below 60

Challenge 2: Adventure Game

Build a simple text adventure:

1. Ask the player to choose a direction (left/right)
2. Use nested conditionals for different paths
3. Each path leads to more choices
4. Create at least 3 levels of decisions

Challenge 3: Password Checker

Design a program that:

1. Asks for a password
2. Checks if it's the correct password
3. If wrong, gives hints using elif statements
4. Limits attempts using a counter variable

You're Doing Great! :star2:

Congratulations on mastering conditionals! You've learned how to:

• Make your programs think and decide
• Use if, elif, and else blocks effectively
• Create complex decision trees with nesting
• Debug conditional logic problems

Conditionals are the foundation of intelligent programs. Every app, game, and website uses them to respond to user actions. You're now ready to create programs that can make decisions just like you do!

:information_source: Next Steps In the next lesson, we'll explore loops - another powerful programming concept that lets your code repeat actions. Combined with conditionals, you'll be able to create even more amazing programs!

Keep experimenting with different conditional structures, and remember - the best way to learn is by trying things out and seeing what happens!