Designing, creating and refining algorithms

Inputs, processes and outputs

Before writing a solution, identify its inputs, the processes performed on them and the outputs the user needs.

Example: calculate a class average

Input: each student's mark.
Process: add the marks and divide by the number of students.
Output: the average mark.

A structure diagram can show how a main task is broken into smaller tasks:

Calculate class average
- Get marks — read each mark
- Calculate total — add the marks
- Calculate average — divide total by count
- Display average — show the result

Key terms

Flowchart symbols

A flowchart shows an algorithm with standard shapes and arrows. The shape helps identify what each step does:

Symbol	Shape	Use
Terminal	Rounded oval	Start or end
Process	Rectangle	Calculation or assignment
Decision	Diamond	A condition with two labelled routes, often Yes and No
Input/output	Parallelogram	Read input or display output
Sub-program	Rectangle with double sides	Call a named sub-program

This chart asks for a mark and displays whether it passes. Follow the arrows in order; the decision's labels tell you which branch to take.

Key terms

Pseudocode, tracing and refining

Pseudocode describes an algorithm in structured, readable steps without requiring every programming-language detail. OCR Exam Reference Language (ERL) has precise syntax; Python is a high-level language. The same logic can be expressed in either:

ERL

INPUT mark
IF mark >= 50 THEN
    OUTPUT "Pass"
ELSE
    OUTPUT "Try again"
ENDIF

Python

mark = int(input("Mark: "))
if mark >= 50:
    print("Pass")
else:
    print("Try again")

A trace table records how variables change at each step. Use it to find a logic error, complete an unfinished algorithm or check a refinement. For input 62, the condition mark >= 50 is true and the output is Pass. Test a different input, such as 40, to check the other branch.

Key terms

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