CS208, Wednesday 12 Jan 2022

Coming up

• Today: integers, byte order, characters, general advice
• Friday: debugging C with gdb

Write these integers in decimal

• 0xA3D =
• 0456 =
• 0b1011101 =

Write these decimal integers as...

• 37 = 0x?
• 37 = 0b?
• 37 = 0?
• 419 = 0x?
• 419 = 0b?
• 419 = 0?

Two's complement integers

• Odometer & counting
• Adding in binary
• Why 2's comp instead of signed magnitude?
• Negating a 2's comp integer
• Converting between 2's comp and decimal

Try it

• 8-bit 2's comp: 0x73 = ? (decimal)
• 8-bit 2's comp: 0x83 = ? (decimal)
• 32-bit 2's comp: 0xFFFFFFA5 = ? (decimal)
• (try that previous one two ways: bit-flipping vs. what to add to get 0)
• -57 = ? (8-bit 2's comp)
• -57 = ? (32-bit 2's comp)

Byte order

• (Here we are again: memory as sequence of addressed bytes)
• How do you store the 32-bit integer 20 = 0x00000014?
• Little-endian
• Big-endian
• Jonathan Swift
• On Holy Wars and a Plea for Peace by Danny Cohen, 1 April 1980

Miscellaneous thoughts

• Amount & importance of reading
  • What Jeff writes
  • Textbook readings
  • Other readings
  • Exams & assignments as values statements
• Using my code samples
  • Run them
  • Read them (what don't you get?)
  • Modify them (play with them)
  • (Sometimes) use them to start assignments
• Questions about either the past or the upcoming C assignments?