Character encoding: convert characters to character codes

The idea

Character encoding gives each character a unique numeric code so a computer can store and process text. To convert a character to its code, identify the character set in use (for example ASCII or Unicode), then look up the numeric value assigned to that character. For instance, in ASCII the capital letter A is stored as the decimal value 65, and the lowercase a is 97. The same character may have different codes in different character sets, so the set must be stated. A reliable method is: take the character, find it in the relevant code table, and record the decimal (or binary/hex) value. This skill underpins how text files, strings and keyboard input are represented in memory.

What earns the marks

• Identifies that each character is mapped to a unique numeric code by a character set such as ASCII or Unicode.
• States the correct code for a named character in a stated character set, e.g. A is 65 in ASCII.
• Recognises that the code depends on which character set is being used.
• Records the value in the required base (decimal, binary or hexadecimal) accurately.
• Explains that the code is what the computer stores for that character.

Common mistakes and how to put them right

• Assuming every character set gives the same code.

  Put it right: Is that codes depend on the character set, so ASCII and Unicode values must be checked separately.

• Confusing the code for uppercase and lowercase letters.

  Put it right: Is that in ASCII uppercase A is 65 while lowercase a is 97.

• Giving a code without stating the character set.

  Put it right: Is to always name the character set so the value is unambiguous.

Exam tips

• Always state which character set you are using before giving a code.
• Learn a few anchor values (such as A = 65 and a = 97 in ASCII) to check your answers.
• If asked for binary or hexadecimal, convert carefully and show the base clearly.