Unit 11.1C · Term 1

Flowcharts

A flowchart is a visual representation of the sequence of steps in an algorithm or process. Unlike DFDs (which show data movement), flowcharts show the order of operations, including decisions and loops.

Learning Objectives

11.2.1.7 Draw and interpret flowcharts for computing systems

Lesson Presentation

11.1C-flowcharts.pdf · Slides for classroom use

View Download

Conceptual Anchor

The GPS Directions Analogy

A flowchart is like GPS turn-by-turn directions. "Go straight" (process), "Turn left at the junction?" (decision — Yes/No), "You've arrived" (end). Each step leads to the next, and decisions create different routes. Flowcharts work the same way for algorithms.

Rules & Theory

Standard Flowchart Symbols

Symbol	Shape	Meaning	Example
Terminator	Rounded rectangle (oval)	Start or End	START, END
Process	Rectangle	Action or calculation	sum = a + b
Decision	Diamond ◇	Yes/No question	Is x > 10?
Input/Output	Parallelogram	Read input or display output	INPUT name, PRINT total
Arrow	→	Flow direction	Connects symbols in order
Connector	Small circle	Joins separate parts of flowchart	Used when flowchart spans pages

Flowchart Rules

#	Rule
1	Every flowchart starts with a START terminator and ends with an END terminator
2	Flow goes top to bottom, left to right (generally)
3	Arrows connect all symbols — no "floating" shapes
4	Decision diamonds must have exactly two outputs: Yes and No
5	Use standard shapes — don't invent your own
6	Write inside symbols, not beside them

Example: Is a Number Even or Odd?

  ╭─────────╮
  │  START   │
  ╰────┬─────╯
       ↓
  ┌──────────────┐
  │ INPUT number │
  └──────┬───────┘
         ↓
     ◇──────────◇
    │ number     │
    │ MOD 2 = 0? │
     ◇──────────◇
    Yes ↓      No ↓
  ┌────────┐  ┌──────┐
  │ PRINT  │  │ PRINT│
  │ "Even" │  │ "Odd"│
  └───┬────┘  └──┬───┘
      └─────┬────┘
            ↓
     ╭──────────╮
     │   END    │
     ╰──────────╯

Example: Sum Numbers Until User Enters 0

  ╭─────────╮
  │  START   │
  ╰────┬─────╯
       ↓
  ┌──────────┐
  │ sum = 0  │
  └────┬─────┘
       ↓
  ┌──────────────┐ ←──────────┐
  │ INPUT number │            │
  └──────┬───────┘            │
         ↓                    │
     ◇──────────◇             │
    │ number     │            │
    │  = 0?      │            │
     ◇──────────◇             │
    Yes ↓      No ↓            │
    │        ┌───────────┐    │
    │        │ sum = sum  │    │
    │        │ + number   │    │
    │        └─────┬─────┘    │
    │              └──────────┘
    ↓
  ┌──────────────┐
  │ PRINT sum    │
  └──────┬───────┘
         ↓
  ╭──────────╮
  │   END    │
  ╰──────────╯

Flowchart vs Pseudocode

Both represent algorithms. Flowcharts are visual — better for understanding flow and presenting to non-programmers. Pseudocode is text-based — better for programmers and closer to actual code.

Common Pitfalls

Using Wrong Shapes

Using a rectangle for input/output is wrong — use a parallelogram. Using a rectangle for decisions is wrong — use a diamond. Each symbol has a specific meaning.

Forgetting the Loop-Back Arrow

In loops, you need an arrow going back up to the loop condition. Without it, the flowchart only runs once — it's not a loop!

Tasks

Remember

Draw all 6 flowchart symbols and label each one.

Apply

Draw a flowchart that inputs a student's mark and outputs "Pass" (≥50) or "Fail" (<50).< /p>

Apply

Draw a flowchart that finds the largest of 3 input numbers.

Analyze

Convert this flowchart problem into pseudocode: Input numbers until -1, counting how many are positive.

Self-Check Quiz

Q1: What shape is used for decisions?

Diamond (◇) — with Yes and No branches.

Q2: What shape is used for input/output?

Parallelogram — used for INPUT and PRINT operations.

Q3: How is a loop shown in a flowchart?

With an arrow going back from a process to a decision diamond (creating a cycle in the flow).