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:

flowchart TD
  A(["Start"]) --> B["INPUT length"]
  B --> C["INPUT width"]
  C --> D["area = length x width"]
  D --> E["OUTPUT area"]
  E --> F(["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):

flowchart TD
  A(["Start"]) --> B["INPUT score"]
  B --> C{"Is score >= 50?"}
  C -->|Yes| D["OUTPUT 'Pass'"]
  C -->|No| E["OUTPUT 'Fail'"]
  D --> F(["Stop"])
  E --> F

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

Example 3: Iteration (WHILE Loop)

A flowchart to keep asking for passwords until the correct one is entered:

flowchart TD
  A(["Start"]) --> B["INPUT password"]
  B --> C{"Is password = 'secret'?"}
  C -->|No| D["OUTPUT 'Try again'"]
  D --> E["INPUT password"]
  E --> C
  C -->|Yes| F["OUTPUT 'Access granted'"]
  F --> G(["Stop"])

Example 4: Count-Controlled Loop (FOR Loop)

A flowchart to output the numbers 1 to 5:

flowchart TD
  A(["Start"]) --> B["counter = 1"]
  B --> C{"Is counter <= 5?"}
  C -->|No| D(["Stop"])
  C -->|Yes| E["OUTPUT counter"]
  E --> F["counter = counter + 1"]
  F --> C

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Drawing Flowcharts in the Exam

Step-by-Step Approach

1. Start with the Start terminator — Always begin here.
2. Identify inputs — What data does the algorithm need? Draw input parallelograms.
3. Add processes — What calculations or operations are performed? Draw rectangles.
4. Add decisions — Where does the algorithm need to make a choice? Draw diamonds with Yes/No exits.
5. Add loops — Where does the algorithm repeat? Draw flow lines going back to earlier symbols.
6. Add outputs — What results does the algorithm produce? Draw output parallelograms.
7. End with the Stop terminator — Always finish here.
8. Check the flow — Follow the arrows to make sure the logic is correct.

OCR Exam Tip: When drawing flowcharts in the exam, use a pencil so you can correct mistakes. Draw the shapes clearly and label all arrows from decisions (Yes/No). Check that every path eventually reaches the Stop terminator. Make sure decisions are phrased as questions with exactly two outcomes.

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Tracing Through Flowcharts

Tracing means following the flowchart step by step with specific input values to determine the output. Use a trace table to track the values of variables at each step.

Example: Trace this flowchart with input 7

flowchart TD
  A(["Start"]) --> B["INPUT x"]
  B --> C["y = x * 2"]
  C --> D{"Is y > 10?"}
  D -->|Yes| E["OUTPUT y"]
  E --> F(["Stop"])
  D -->|No| G["OUTPUT x"]
  G --> H(["Stop"])

Trace:

Step	x	y	Decision	Output
1	7	-	-	-
2	7	14	-	-
3	7	14	14 > 10? Yes	-
4	7	14	-	14

Output: 14

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Common Flowchart Exam Questions

Question Type	What To Do
Draw a flowchart	Design the algorithm and draw it using correct symbols
Trace a flowchart	Follow the steps with given input values, use a trace table
Identify the output	Trace through and state what the algorithm outputs
Find errors	Look for incorrect logic, missing paths, or wrong symbols
Explain what the flowchart does	Describe the algorithm's purpose in plain English

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Summary

Flowcharts are visual representations of algorithms using standard symbols: terminators, processes, decisions, input/output, and flow lines. They show sequence, selection, and iteration clearly. For the OCR J277 exam, make sure you know all the symbols, can draw flowcharts for given problems, and can trace through flowcharts to determine outputs. Always use correct symbols and label decision exits clearly.

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Worked Example: Shop Loyalty Discount

A shop awards discounts at the checkout based on the value of the basket and whether the customer holds a loyalty card:

• Basket under £20: no discount.
• Basket £20 or more, no loyalty card: 5% discount.
• Basket £20 or more, with loyalty card: 10% discount.

Draw a flowchart that inputs the basket total and a Boolean indicating whether the customer has a loyalty card, then outputs the final amount to pay.

flowchart TD
    A([Start]) --> B[/INPUT total/]
    B --> C[/INPUT hasCard/]
    C --> D{total >= 20?}
    D -- No --> E[finalAmount = total]
    D -- Yes --> F{hasCard = true?}
    F -- Yes --> G[finalAmount = total * 0.90]
    F -- No --> H[finalAmount = total * 0.95]
    E --> I[/OUTPUT finalAmount/]
    G --> I
    H --> I
    I --> J([Stop])

Why this flowchart earns full marks: