Stretch tasks Character Encoding

Round 1: Quiz Blitz

1. 128 2 to the power 7 is 128, numbered 0 to 127.
2. 90 Z is 25 letters after A: 65 + 25 = 90.
3. 99 a 97, b 98, c 99.
4. 55 48 + 7 = 55. The character '7' is not the number 7.
5. Add 32 'A' is 65 and 'a' is 97: always 32 apart.
6. False In a variable-width encoding, plain English costs the same as ASCII.
7. It was displayed using a different character set Both ends must use the same character set.
8. Arabic letters; Chinese characters ASCII was designed for English.
9. A code that causes an action, such as a new line Carriage return is a control character: it does something rather than print a symbol.
10. 256 8 bits give 2 to the power 8 = 256 codes.
11. Because everybody agreed it would be A character set is an agreement, not a property of the machine.
12. True So older ASCII files still open correctly.

Round 2: Quick Fire

1. • The code for '0' is 48, and the digits are in order
   • Subtract 48 from the code: 55 - 48 = 7
   Model answer

   The digit characters are in order, starting with '0' at 48. So subtract 48 from the code: '7' has the code 55, and 55 - 48 = 7.

2. • Unicode represents far more characters, covering every language
   • But it can use more bits per character, so more storage
   Model answer

   Unicode represents far more characters than ASCII, over a million, covering every writing system, but it can use more bits per character, so text can take more storage.

3. • A character set gives each character an agreed code
   • With a different set, the codes would show as the wrong characters
   Model answer

   A character set gives each character an agreed code. If the other computer used a different set, the same codes would be shown as the wrong characters, such as boxes and question marks.

4. • Find its code, for example with CHAR_TO_CODE
   • Add 32, then turn the new code back into a character
   Model answer

   Find the letter's code with CHAR_TO_CODE, for example 65 for A. Add 32, then turn the new code back into a character with CODE_TO_CHAR: 97 is a.

Round 3: Big Think

1. • ASCII uses 7 bits, so it has only 128 codes
   • ASCII was designed for English, with no Greek, Arabic or Chinese
   • Unicode uses more bits, giving over a million codes
   • The trade-off: more storage for characters outside the basic set
   • Its first 128 codes match ASCII, so old files still work
   Model answer

   ASCII uses 7 bits, so it has only 128 codes, and it was designed for English: it has no codes for Greek, Arabic, Chinese or Hindi. Unicode uses more bits per character, giving room for over a million codes, enough for every writing system. The trade-off is size: characters outside the basic set take more bytes, so documents can need more storage. Its first 128 codes are the same as ASCII, so older files still open correctly.

2. • Letters are in sequence: 'A' is 65, 'B' is 66
   • Lower case is always 32 more, so 'a' is 97
   • '0' is 48
   • So a digit's value is its code minus 48, such as 55 - 48 = 7
   Model answer

   The letters are in sequence: 'A' is 65, 'B' is 66, and so on. Lower case is always 32 more than upper case, so adding 32 to 65 gives 97, which is 'a'. The digit characters start at '0', which is 48, so a digit's value is its code minus 48: the character '7' is 55, and 55 - 48 = 7.

This or That

1. No: '7' is code 55 That is why input must be cast before arithmetic.
2. Unicode ASCII uses 7 or 8 bits. Unicode uses from 8 to 32.
3. Carriage return A control character makes something happen rather than printing a symbol.
4. 98 Lower case is always 32 more: 66 + 32 = 98.
5. Unicode's first 128 codes match That was a deliberate design choice.
6. The same space as ASCII The basic characters need only one byte each.
7. 7 Extended ASCII uses 8.
8. A menu written in Greek ASCII has no Greek letters.

Memory Match

• A 6 ASCII: 7 bits, 128 codes
• B 4 Extended ASCII: 8 bits, 256 codes
• C 2 Unicode: Over a million codes, every script
• D 1 'A': 65
• E 3 'Z': 90
• F 5 '0': 48

Sort It

1. Digit character 55 55 is the character '7'.
2. Upper case letter 65 65 is A, the first upper case letter.
3. Digit character 50 50 is the character '2'.
4. Lower case letter 122 122 is z: 90 + 32.
5. Upper case letter 90 90 is Z, the last upper case letter.
6. Upper case letter 72 72 is H.
7. Digit character 48 48 is the character '0'.
8. Lower case letter 110 110 is n.
9. Upper case letter 77 77 is M.
10. Lower case letter 100 100 is d.
11. Digit character 57 57 is the character '9', the last digit.
12. Lower case letter 97 97 is a: 65 + 32.