User Defined Data Types

• This is chapter 10 in your book, you should read it.
• In the 130 you learned about a number of atomic or simple data types.
  • They are called atomic because they can not be broken into any smaller components.
• Look at these types.
  • 
    • From page 463
  • What are these different types?
    • This is actually a subset of the types.
    • See this page for more details.
  • What is the domain of each of these types?
    • Look in /usr/include/limits.h
    • A character is 8 bits.
      • Due to historical reasons.
      • Based on the ACSII table.
      • A a somewhat better reference
      • Or try man ascii at the linux command line.
    • A character can then represent
      • Signed:
        • $ -2^{(8-1)} $ to $2^{(8-1)}-1 $
        • or $ -2^7$ to $2^7-1 $
        • or -128 to 127
      • Unsigned:
        • Why does unsigned exist?
        • 0 to $ 2^{8}-1 $
        • or 0 to 255
      • Look at char.cpp
        • note when we compile this, the compiler warns us that this is a bad idea.
        • sizeof gives the size of a type or expression in bytes
          • This returns a size_t.
          • A size_t is probably an unsigned int or long.
          • But it is a positive number
          • Why does this exist?
  • What are the operations on each of these types?
    • See the bottom of the page of this reference.
    • Or appendix B of your book.
  • What are the relationships between the various sub types of a given type?
    • We know that a char is a byte. (by definition)
      • This is at least 8 bits.
      • But could be larger based on the architecture of the system
    • The standard says that a short is at least as big as a char, but perhaps longer.
    • sizeof(long long) >= sizeof(long) >= sizeof(int) >= sizeof(int) >= sizeof(short) >= sizeof(char) >= 8.
    • Look at sizes.cpp
  • What type form the above chart are we missing?
    • enum : an enumerated type
      • More on this in just a bit.
• We will expand on the basic types the rest of the semester
  • 
  • From Page 490
  • What types that we know about are missing from this chart?
• Character Math
  • Characters are an integer type.
  • We can do math on them.
  • One of the really nice properties of the ASCII, and the UNICODE table in general is the structure.
    • The value for 0 is 48
    • The value for 1 is 49
    • The value for 2 is 50 ...
    • They are all sequential.
  • Thus if we have an ascii digit, we can convert it to it's "integer" value by subtracting '0'
    • The ascii code for '7' is 55.
    • The ascii code for '0' is 48.

    •  '7' - '0' = 55 - 48 
                 = 7

  • This is true for the lower case letters and the upper case letters as well.
    • What is 'a'+3?
    • What is 'X'-2?