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Lesson 6 Decision
Objective Describe the decision construct.

Decision Construct in Procedural Programming

Most programs have statements that are to be executed only under certain conditions. The decision[1] construct (also referred to as the selection construct) allows you to do this. For example, consider the following modified version of the GoForARide program: 
Put on cycling clothes
If the weather is cold
  Put on a jacket
  Put on tights
Go for a ride
Remove cycling clothes
Take a shower

In this program the statements:
Put on a jacket
Put on tights

are executed only when the weather is cold. This is indicated in the pseudocode by indenting these two statements beneath the decision statement:
If the weather is cold

In the next lesson we will look at the repetition construct.
Here is a flowchart for this program. Note how the decision construct allows us to modify the straight sequential flow of execution of a program.

Decision construct allows us to modify the straight sequential flow of execution of a program
The image is a flowchart that outlines the decision-making process for a cyclist preparing for a ride, especially in regard to cold weather. Here's a step-by-step analysis of the flow:
Flowchart Description:
  1. Start: "Put on cycling clothes"
    • This is the first action, and it initiates the process.
  2. Decision Point: "Weather is cold?"
    • A diamond-shaped decision node checks the weather condition.
  3. If "Yes":
    • The flow splits rightward and includes two sequential actions:
    • "Put on a jacket"
    • "Put on tights"
  4. Then continues to: "Go for a ride"
  5. If "No":
    • The flow moves directly down to:
    • "Go for a ride"
  6. Post-ride sequence (for both Yes and No paths):
    • "Remove cycling clothes"
    • "Take a shower"

Key Observations:
  1. The flowchart uses a combination of decision nodes and action steps.
  2. It shows a clear branching logic based on weather conditions.
  3. Actions converge again after the "Go for a ride" step, making the process unified regardless of temperature after that point.
Decision construct allows us to modify the straight sequential flow of execution of a program
Here is the equivalent PlantUML code that recreates the cycling flowchart you provided: 
@startuml
start

:Put on cycling clothes;

if (Weather is cold?) then (Yes)
  :Put on a jacket;
  :Put on tights;
endif

:Go for a ride;
:Remove cycling clothes;
:Take a shower;

stop
@enduml

🛠 To render this:
  • Use a PlantUML editor (e.g., PlantUML Live or PlantText).
  • Paste the code in and click "Refresh" or "Render" to see the flowchart.

[1]Decision: Control flow construct in which a task is performed conditionally. Also referred to as selection.

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