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L5: Conditions & Decisions

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Overview​

In this lesson, students will learn how computers make decisions using conditions.

Programs often need to ask questions such as:

  • Is a button pressed?
  • Is a number larger than 5?
  • Is the room too dark?
  • Is a touch pad being touched?

Computers answer these questions using conditions that become either:

  • TRUE
  • FALSE

Students will use:

  • if statements
  • comparison operators
  • variables
  • random numbers
  • touch sensing

to create interactive programs and build a Rock Paper Scissors game.

Learning Goals​

Students will:

  • understand TRUE and FALSE conditions
  • compare numbers and variables
  • use if statements
  • detect touch input on Pin 1
  • generate random numbers
  • build a simple decision-based game

Time Required​

30–45 minutes

Materials​

  • CincoBit or PixoBit
  • USB cable
  • Computer or Chromebook
  • MicroBlocks

Teacher Notes​

This lesson introduces one of the most important ideas in computer science:

Computers make decisions by checking conditions.

Students should understand:

  • conditions evaluate to TRUE or FALSE
  • programs compare numbers and variables
  • if statements only run code when a condition is TRUE

This lesson combines:

  • logic
  • variables
  • events
  • touch sensing
  • randomness

into a complete interactive project.

What is a Condition?​

A condition is a question that has only two possible answers:

  • TRUE
  • FALSE

Examples:

  • Is 10 greater than 5?
  • Is the button pressed?
  • Is the score equal to 100?

Programs use these answers to decide what to do.

TRUE and FALSE​

Conditions are evaluated by the computer.

Examples:

QuestionResult
Is 5 greater than 3?TRUE
Is 2 greater than 10?FALSE
Is 7 equal to 7?TRUE
Is 4 less than 1?FALSE

Comparison Operators​

Programs compare numbers and variables using comparison operators.

OperatorMeaning
=equal to
>greater than
<less than

Examples:

ExpressionResult
score > 10TRUE if score is larger than 10
count = 5TRUE only if count is exactly 5
temperature < 20TRUE if temperature is below 20

Using IF Statements​

An if statement tells the computer:

“Only run this code if the condition is TRUE.”

Example:

if score > 5

If the condition is TRUE:

  • code inside the block runs

If the condition is FALSE:

  • the code is skipped

Step 1 - Using Variables with Conditions​

Create a variable called score. If not sure how, go back to the Variables lesson. Bring in the set block into the workspace to set the variable to 7.

Add if block from the Control palette, and inside of it add the "larger than" block > from the Operators palette.

You can now add whatever blocks inside the if block to execute only if the evaluation is TRUE. In this case it is true, as the score is more than 5.

if true

We used the say block from the output palette. This block is useful for "Debugging", for checking and seeing what the program is doing. It will only do something when the device is connected to MicroBlocks.

Remember, you can simply click on the blocks to run them.

Because 7 is greater than 5:

  • the condition becomes TRUE
  • the code inside the if block runs
  • the say block will execute and show the text.

The if block also allows for running blocks if the condition is FALSE. In English: if condition is true then do this, else do that.

Click on the little arrow at the bottom of the if block. This will reveal the else block. We will change score to 4, which is less than 5.

if else

Try changing the value of score and observe the outcome. What do you think will happen if score is set to 5?

Step 2 - Random Numbers​

Computers can generate random values.

Random numbers are used in:

  • games
  • dice
  • simulations
  • selecting winners

Generate a random number:

  • between 1 to 10
  • check if the number is more than 5
  • say the results

The random block found under Operators palette returns a random number between 2 values. You can just click on the block to run it and see what values it is returning. Change the 2 limit value to see what numbers can be generated.

Go to the previous sample and use a random number to set the variable.

if random

We also used multiple items with the say block this time. You can do that by clicking the little right arrow on the say block.

Step 3 - Rock Paper Scissors​

Students will build a simple game.

When A is pressed:

  1. generate a random number
  2. check the value using if statements
  3. display:
    • Rock
    • Paper
    • Scissors

Example Game Logic:

Random NumberResult
1Rock
2Paper
3Scissors

rock paper scissors

PixoBit Version

Display:

  • graphics
  • scrolling text
  • animated results

Ideas:

  • “ROCK!”
  • “PAPER!”
  • “SCISSORS!”

Students can create:

  • menus
  • scoreboards
  • animated transitions

Understanding Decision Making​

Computers constantly evaluate conditions and make decisions.

Examples:

  • automatic doors
  • elevators
  • thermostats
  • games
  • traffic lights
  • phones

Programs react differently depending on whether conditions are TRUE or FALSE.

Troubleshooting​

  • Wrong game result appears
    • check comparison values carefully
  • Nothing happens
    • verify there is a running loop
    • check what is inside the if block

Vocabulary​

WordMeaning
ConditionA TRUE/FALSE question
TRUECondition matches
FALSECondition does not match
IF StatementRuns code only when a condition is TRUE
Comparison OperatorChecks values
Random NumberA value chosen unpredictably

Wrap-Up Question​

Why are conditions important for games and interactive devices?