User Defined Data Types, Part 1

• We have this diagram from chapter 3 of the book
• 
• She defines simple types as a data type in which each value is atomic or indivisible.
  • An int, 3, can not be broken down any further.
  • But a string "bob" has three character components.
  • We have looked at most of the simple types
• A few bits she discusses here
  • sizeof (type or expression)
    • returns the size of the argument in bytes.
    • Write a quick demo program.
  • limits.h or climits
    • INT_MIN, INT_MAX, LONG_MIN, LONG_MAX, ...
  • Characters
    • Represented internally as an int, two's compliment.
    • printed according to the ascii chart. (man ascii)
• User Defined Types, sort of
  • Sometimes it is nice to be able to provide your own name to a data type.
  • This is probably not as useful here, but this is where she covers it.
  • typedef existing_type new_type;
  • typedef int number;
  • The identifier number
    • Can now be used anywhere a type is permitted
    • Is now equivalent to the type int
  • This is generally done in the global declaration area, before it will be used.
  • It is not common to provide a typedef for a simple type, but it can be done.
  • Here is a somewhat silly example
    • ON the BBC program The Code, they introduce an equation that models population. If n is the current population represented as a percent of the maximum population, and R is a reproduction rate, n_next = R×n×(1-n). This is apparently good when r is about 2. A chaotic system arises when R is closer to 4. Apparently lemmings have a reproduction rate that 3.57, which gives rise to chaos. Write a program which simulates the population of lemmings.
    • There is a discussion of this here and a wikipedia page as well.
    • I am not sure the type I want to represent the population, float, double or long double, so I will do a typedef float PopulationT
    • While it is not a requirement, I find ending a type with a T helps me detect that it is a type and not a constant, function, or variable.
    • For expedience I will just hard code the initial population and the value of R.
    • Here is one version of the code