Flowcharts: Symbols, Conventions, and Drawing

This lesson covers flowcharts as a method for representing algorithms, as required by OCR J277 Section 2.1. Flowcharts are a visual way to show the step-by-step logic of an algorithm, including decisions and loops.

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What Is a Flowchart?

A flowchart is a diagram that represents an algorithm using standard symbols connected by arrows (flow lines). Flowcharts show the sequence of steps, decision points, and flow of control in an algorithm.

Flowcharts are useful because they:

• Provide a visual representation of logic
• Make it easy to see the flow of an algorithm
• Clearly show decisions and loops
• Are language-independent — anyone can understand them

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Standard Flowchart Symbols

You must know these standard symbols for the OCR J277 exam:

Symbol	Shape	Purpose	Example
Terminator	Rounded rectangle (oval)	Start or end of the algorithm	"Start" / "Stop"
Process	Rectangle	A step or action	"total = total + number"
Decision	Diamond	A question with Yes/No (True/False) outcomes	"Is score > 50?"
Input/Output	Parallelogram	Receiving input or producing output	"INPUT name" / "OUTPUT total"
Flow line	Arrow	Shows the direction of flow between symbols	Connects symbols
Subroutine	Rectangle with double side lines	Call to a separate procedure/function	"CALL calculateTotal()"

OCR Exam Tip: The most common mistake is using the wrong shape. Rectangles are for processes (calculations, assignments). Parallelograms are for input/output. Diamonds are ONLY for decisions (yes/no questions). Make sure you draw the correct shapes in the exam.

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Flowchart Conventions

Convention	Detail
Every flowchart has one Start and one Stop	Use terminators (ovals)
Arrows show direction of flow	Flow goes downward by default, with arrows indicating any changes
Decisions have exactly two exits	Labelled "Yes" and "No" (or "True" and "False")
Each symbol has one entry point	Except decisions which have one entry and two exits
Write inside the symbols	Instructions, conditions, or labels go inside the shapes
Keep it clear and neat	Use straight lines, avoid crossing arrows where possible

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Flowchart Examples

Here is an example flowchart for checking whether a number is even or odd:

flowchart TD
    A([Start]) --> B[/INPUT number/]
    B --> C{number MOD 2 = 0?}
    C -- Yes --> D[/OUTPUT 'Even'/]
    C -- No --> E[/OUTPUT 'Odd'/]
    D --> F([Stop])
    E --> F

Example 1: Sequence (Simple Calculation)

A flowchart to calculate the area of a rectangle:

[Start]
   |
[INPUT length]
   |
[INPUT width]
   |
[area = length x width]
   |
[OUTPUT area]
   |
[Stop]

Symbols used: Terminator (Start, Stop), Input/Output (INPUT, OUTPUT), Process (calculation)

Example 2: Selection (IF...ELSE)

A flowchart to check if a student has passed (score >= 50):

[Start]
   |
[INPUT score]
   |
<Is score >= 50?>
  / \
Yes   No
 |     |
[OUTPUT  [OUTPUT
"Pass"]  "Fail"]
 |     |
  \ /
[Stop]

Symbols used: Terminator, Input/Output, Decision (diamond), Process (output)