AQA · GCSE · Computer Science
Course version: 8525 · Version from Sept 2020
Understand that character codes are commonly grouped and run in sequence…
Full specification wording
Character encoding: Understand that character codes are commonly grouped and run in sequence within encoding tables.
An encoding table maps each character to a numeric code.
Checked against the AQA 8525 specification (opens in a new tab) on .
- Point 8 of 10
Study notes
From the checked teaching notes for this specification point.
The idea
An encoding table maps each character to a numeric code. In common encodings such as ASCII, these codes are not scattered randomly: characters are collected into groups, for example all the capital letters together, all the lower case letters together and all the digits together. Within each group the codes run in sequence, so consecutive characters have consecutive codes. This means a table has structure you can rely on: if you know one code in a group, you can predict the codes of the others by counting forward or backward. Recognising this grouping and sequencing helps you look up codes quickly, check whether a value looks plausible, and work out codes that are not shown in a short extract of a table.
What earns the marks
- States that an encoding table maps characters to numeric codes.
- States that character codes are commonly organised into groups, e.g. capitals, lower case letters and digits.
- States that within a group the codes run in sequence (consecutive characters have consecutive codes).
- Explains that knowing one code in a group allows other codes in that group to be predicted by counting.
- Applies the idea to check or deduce a code from a table extract rather than treating each code as unrelated.
Common mistakes and how to put them right
Treating each character code as independent and random.
Put it right by explaining that codes are grouped and sequential within an encoding table.
Assuming the sequence continues unbroken across different groups.
Put it right by noting each group (capitals, lower case, digits) is a separate block.
Thinking a short table extract lists every possible code.
Put it right by explaining that the sequential pattern lets you deduce codes not shown.
Exam tips
- Look for the pattern of consecutive codes rather than memorising individual values.
- Identify the group a character belongs to before predicting its code.
- Use a known code as an anchor and count forward or backward to the target character.
Try the lesson
The start of the Character encoding: Understand that character codes are commonly grouped and run in sequence within encoding tables. lesson, made from checked teaching notes for this specification point.
Have a go first
In a character set where the code for 'A' is 65 and the codes for the uppercase letters run in sequence, what is the code for 'D'?
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