Students should be able to use a given character encoding table to:

The idea

A character encoding table pairs each character with its binary code. Learners must use a supplied table rather than memorise it. The skills are: find the code for a given character, find the character for a given code, and encode or decode a short string by looking up each character in turn and joining the codes in order. For example, to encode a word, take each letter, read its binary code from the table and write the codes in sequence; to decode, split the binary into the code length shown in the table and match each group to a character. Always use the exact table provided, keep the code length consistent, and preserve the order of characters, because a different table or wrong grouping produces different text.

What earns the marks

• Locates the binary code for a specified character by reading across the supplied table.
• Identifies the character matching a given binary code by reading the table in reverse.
• Encodes a short string by looking up each character and writing the codes in the original order.
• Decodes a binary string by splitting it into the code length used in the table and matching each group.
• Keeps the code length and character order consistent so the decoded text matches the original.

Common mistakes and how to put them right

• Using remembered codes instead of the supplied table.

  Put it right by reading values directly from the given table.

• Splitting a binary string into the wrong group length.

  Put it right by checking the code width stated in the table before grouping.

• Reordering characters when joining codes.

  Put it right by encoding each character strictly left to right in the original sequence.

Exam tips

• Read the table header to confirm the code length before splitting any binary string.
• Work character by character and write each code separately to avoid losing your place.
• Check your answer by decoding it back with the same table to confirm it matches.