CptS 121 Fall 09 Lecture 81

1
CptS 121 Fall 09 Lecture 8-1

• HK Chapter 7.1 7.3 Data Types
• Lecture Outline
• Representation of numeric and char types
• Enumerated Types
• Quiz (on material covered last week)

2
Internal Representation of int and double

• As we already learned, int and double have
  different internal formats

3
Internal Representation of int and double (cont.)

• C supports a variety of different integer formats

4
Internal Representation of int and double (cont.)

• Likewise, C supports a variety of different
  double formats

5
Internal Representation of int and double (cont.)

• Beware of round-off errors!
• Don't rely on two floating-point values being
  equal
• for (trial 0 trial ! 10.0 trial 0.1)
• Even the following may not execute the same
  number of times on all computers
• for (trial 0 trial lt 10.0 trial 0.1)
• It's better to use integers as loop counters!

6
Internal Representation of int and double (cont.)

• Conversions between int and double
• When we assign an int to a double or a double to
  an int, C performs an automatic conversion
• int k 5, m 4, n
• double x 2.5, y 4.1, z
• z k x / 7.5 k is converted to double
  prior to /
• z k / m / k / m is evaluated first result
  (1) is then converted to double
  (1.0) /
• n x y / x y is evaluated first (10.25).
  Result is then converted to int
  (10). Fractional part is lost /

7
Internal Representation of int and double (cont.)

• Conversions between int and double (cont.)
• Note that explicit casting is always an option
• int k 5, m 4, n
• double x 2.5, y 4.1, z
• z (double) k x / 7.5 /
• z (double) k / (double) m / 1.25 /
• n (int) x (int) y / 8 /
• But such casts do not change the internal
  representation of a variable
• printf(.2f\n", (double) k) / 5.00 /
• printf("4d\n",k) / 5 /
• / After these statements are executed, k is
  still stored as the int 5 /

8
Internal Representation of char

• As we have learned, char variables are stored in
  8 bit ASCII (American Standard Code for
  Information Interchange) format
• '0' .. '9' 48 57
• 'A' .. 'Z' 65 90
• 'a' .. 'z' 97 122
• Printable characters 32 122
• Non-printable characters 0 31 and 127
• See Appendix A for the details

9
Internal Representation of char (cont.)

• It is possible to cast between char and int
• int char_codefor (char_code (int) 'A'
• char_code lt (int) 'Z'
• char_code)
• printf("c", (char) char_code)
• Yields the following
• ABCDEFGHIJKLMNOPQRSTUVWXYZ

10
Enumerated Types

• Often, we'd like to define our own custom data
  types
• days of the week
• months of the year
• household budget categories
• business inventory categories
• etc.
• C enumerated types allow us to do this
• typedef enum
• clothing, household, electronics, garden,
• health_beauty, sporting_goods
• inventory_t
• Note clothing gets integer value 0, household
  gets integer value 1, . . . sporting_goods gets
  integer value 5

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Enumerated Types (cont.)

• Once we've defined an enumerated type, we can
  declare variables of that type
• inventory_t inventory_kind
• and use the type in switch statements
• void print_inventory(inventory_t inv_kind)
• switch (inv_kind)
• case clothing
• printf("clothing")
• break

12
Enumerated Types (cont.)

• case household
• printf("household")
• break
• case electronics
• printf("electronics")
• break
• case garden
• printf("garden")
• break
• case health_beauty
• printf("health and beauty")
• break
• case sporting_goods
• printf("sporting goods")
• break

13
Enumerated Types (cont.)

• We can make direct comparisons
• if (household lt sporting_goods) / true /
• if (electronics ! health_beauty) / true /
• if (garden lt household) / false /
• and "scroll" through items
• inventory_t this_inventory household
• while (this_inventory lt sporting_goods)
• print_inventory(this_inventory)
• this_inventory

14
Enumerated Types (cont.)

• We can even cast enumerated types to int
• int household_val
• inventory_t this_inventory
• household_val (int) household / 0 /
• ..and cast integers to the enumerated type
• this_inventory (inventory_t)(electronics 1)
  / garden /