Algorithm Flowcharts with Mermaid

Use Mermaid to sketch decision logic before coding. A clear flowchart reduces guessing and makes Python conditions easier to implement.

Quick Workflow

define the program goal in one sentence
list inputs and expected outputs
map decision points (if/elif/else) as branches
check every decision has a path for invalid input
translate each branch into Python code

Mermaid Starter Template

flowchart TD
  A[Start] --> B[Collect Input]
  B --> C{Valid?}
  C -->|Yes| D[Process]
  C -->|No| E[Show Error]
  E --> B
  D --> F[Output Result]
  F --> G[End]

🧠 Mermaid.live – Building an Algorithm flow chart

Mermaid turns diagram code into a flowchart. You write the structure. Mermaid builds the shapes.

🚀 Step 1: Open Mermaid.live

https://mermaid.live

Left = code editor
Right = diagram preview

🎯 What this example models

This example shows how a while loop works:

Start
Ask for a number
Check if number is < 5
If yes → add 1 and repeat
If no → end

The arrow that goes back to the decision creates repetition.

🔷 Shape Guide

([ ]) → Start / End

[ ] → Process

{ } → Decision

[/ /] → Input / Output

🖼 Example Flow chart

Notice how the decision has two labelled paths and one returns back to repeat.

⌨ Step 2: Paste This Code

Show/Hide Mermaid Code

flowchart TD
    A([Start]) --> B[/Enter a number/]
    B --> C{Is number < 5?}
    C -- Yes --> D[Add 1 to number]
    D --> C
    C -- No --> E([End])

Checkpoint: Your diagram should show a loop returning to the decision box.

🛠 Assessment Practice Challenge – Booking Validation

Now design your own algorithm flow chart.

Create a flowchart for a booking system that:

• Asks for the user’s name
• Asks what type of pet they have (cat or dog)
• Repeats the question if the input is invalid
• Assigns a price based on the pet type
• Displays a confirmation message
• Ends

Think carefully:
Where is the loop?
What controls it?
Where is the price set?
Are all decision paths labelled?